Photo-addressable type recording display apparatus

ABSTRACT

A photo-addressable type recording display apparatus realizes high sensitivity recording display and realizes recording display with short writing pulse application time. The photo-addressable type recording display apparatus is provided with a recording unit that displays an image, a light writing unit that writes an image in the recording unit by the pattern of light, and a control unit that controls the recording unit and the light writing unit. The recording unit is provided with a spatial light modulation element and a driving unit, and the spatial light modulation element has a memory liquid crystal display element layer and organic photoconductive switching element layer. The control unit determines the magnitude and the application time of a voltage that is applied on the spatial light modulation element by the driving unit so that the threshold voltage corresponds to the voltage waveform determined correspondingly to the comparative magnitude relation between the time constant D of the liquid crystal display element layer and the time constant S of the organic photoconductive switching element layer during non-irradiation with light and irradiation with light by the light writing unit, and supplies a trigger signal for driving waveform output to the driving unit.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a photo-addressable type recordingdisplay apparatus, and more particularly relates to a photo-addressabletype recording display apparatus provided with a light switching elementand a display element combined together.

[0003] 2. Description of the Related Art

[0004] Recently, a photo-addressable type spatial light modulationdevice provided with functional elements such as photoconductive lightswitching element and a display element that are combined together hasbeen developed, and has been used practically as a light valve of aprojector. Furthermore, it is tried to use it in the optical informationprocessing field as described in “Liquid crystal spatial light modulatorand information processing” EKISHO, Vol. 2, No. 1, 1998, pp. 3-18.

[0005] Furthermore, for example, as described in H. Yoshida, T.Takizawa, et al., “Reflective Display with Photoconductive Layer and aBistable, Reflective Cholesteric Mixture” SID, 1996, APPLICATION DIGEST,pp. 59, a recording display medium provided with a display elementformed of cholesteric liquid crystal and a light switching elementformed of amorphous silicon and Elgraphy system that is an image inputsystem formed of laminated memory liquid crystal and organicphotosensitive material have been studied as a photo-addressable typerecording display medium.

[0006] As the display material used for the display element of suchphoto-addressable type recording display medium, various liquid crystalmaterial such as nematic liquid crystal, twist nematic liquid crystal,super twist liquid crystal, and smectic liquid crystal,surface-stabilized ferroelectric liquid crystal, polymer dispersionliquid crystal that is formed by polymer-dispersing the liquid crystalmaterial as described hereinabove, and capsulated liquid crystal that isformed by capsulating the liquid crystal material as describedhereinabove have been known.

[0007] A photo-addressable type recording display medium provided with adisplay element formed of memory display material is capable of holdingthe display state without electric power for holding the recordingdisplay. Therefore, because the display state is held even if thedisplay medium is detached from a writing apparatus after the digitalinformation has been recorded and displayed, it is possible to carryaway the display medium that has been detached from the writingapparatus, and such display medium has been attract much attentions asan electronic paper medium.

[0008] For example, cholesteric liquid crystal, ferroelectric liquidcrystal, polymer dispersion liquid crystal, and capsulated liquidcrystal have been known as memory display material, and application ofthese display material to a recording display medium that is detachablefrom a power source has been studied.

[0009] Particularly, a filter used for color selection is unnecessaryfor cholesteric liquid crystal or cholesteric capsulated liquid crystalthat is formed by capsulating cholesteric liquid crystal because of itsselective reflectibility, and also color display is realized by use ofan external single electrode, these display element material hasattracted much attentions because of advantages described hereinabove.

[0010] On the other hand, amorphous silicon (referred to as a-Si:Hhereinafter) that has been proposed as an electronic photographicphotosensitive material and has been used practically and organicphotosensitive material (referred to as OPC hereinafter) have been knownas the element used for a light switching element of a photo-addressabletype recording display medium. The photosensitive material such as Seand CdS is not used currently though these are usable for a lightswitching element, because these are severely harmful for theenvironment and human body.

[0011] a-Si:H has been used practically as photosensitive material forelectronic photography and the high sensitivity and high hardness arecharacteristic of a-Si:H. However, a-Si:H is disadvantageous in that themanufacturing cost is high because a large scale facility is necessaryfor manufacturing because it is manufactured by chemical vapordeposition and the film depositing speed is as low as several μm/h. Asthe result, a-Si:H is replaced by OPC because of its low cost and highsensitivity.

[0012] A general schematic structure of a photo-addressable typerecording display medium provided with such display element and lightswitching element is shown in FIG. 12. In FIG. 12, the photo-addressabletype recording display medium 70 has a laminate structure in which aconductive substrate 60, a charge generation layer (CGL) 62 formed ofOPC placed on the conductive substrate 60, and a charge transfer layer(CTL) 64 formed of OPC are laminated in the order from the bottom. Thecharge generation layer 62 functions as a light switching element layerand generates holes and electrons in the layer when it is irradiatedwith a light. The charge transfer layer 64 is formed of OPC thatfunctions to transfer electrons, and functions to transfer holes orelectrons generated in the charge generation layer 62 in one-way or intwo-way fashion.

[0013] In the case that an image is to be formed by use of the recordingdisplay medium 70 having the structure as described hereinabove, atfirst ions are charged on the surface of the charge transfer layer 64side, and the surface is irradiated with a light having the distributioncorresponding to the image data. When the surface is irradiated with thelight, holes and electrons are generated in quantity corresponding tothe light quantity. The one of generated holes and electrons isattracted to the ions charged on the surface of the charge generationlayer 62, moves toward the surface side of the charge generation layer62, and offsets the charges of ions on the surface.

[0014] In other words, charges on the part irradiated with the light isextinguished and on the other hand charges on the part not irradiatedwith the light remains unchanged. Thereafter, when charged toner issupplied on the charge transfer layer 64 side surface, toner remainsonly on the part where the charge remains, and the toner image thatremains on the charge transfer layer 64 side surface is transferred andfixed on a recording medium to thereby obtain an image.

[0015] Elgraphy system (referred to as Elgraphy hereinafter) that uses adisplay medium having the structure as described hereinabove as arecording display medium for an electrostatic image recording system isproposed in Japan Hardcopy, 1996, Fall Meeting, pp. 25.

[0016] The Elgraphy is an alternative to development system inphotography, and has attracted much attention as a system used forreproducing an image that has been easily taken by a camera at highaccuracy. In the Elgraphy, a recording display medium is formed bycombining a liquid crystal layer formed of memory liquid crystal and anOPC layer together. The OPC layer, which is used as a light switchingelement, functions to apply a DC voltage on the recording display mediumand to selectively irradiate the recording display medium with a lightto thereby generate charges in the OPC layer. The OPC layer transfersthe charges to the liquid crystal layer and applies an electric field onthe liquid crystal layer to thereby orient liquid crystal molecules, andthus the storable image is displayed.

[0017] The Elgraphy is used exclusively for recording mainly and notused for rewriting, but it is possible to rewrite an image. In the casethat an image is to be rewritten, the image is erased thermally asdescribed in, for example, Japan Hardcopy, 1996, Fall Meeting, p25, andthe recording processing described hereinabove is performed again.

[0018] However, the Elgraphy having the structure as describedhereinabove is involved in problem in repetitive recording because theAC driving is not effective. In detail, because electron attractivematerial or electron donating material is used as the chargetransportable material of the charge transport layer usually, only anyone of electron or hole is transported through the charge transportlayer. Therefore, a light switching element having such charge transportlayer functions as a rectifier.

[0019] Therefore, it is difficult to apply the electric field of onepolarity out of the electric fields of the positive and negativepolarity, it is substantially equivalent to the application of DC biason the liquid crystal. As the result, ions in the liquid crystal movesto the place near the electrode by means of action of the bias, theelectric field thereby generated near the electrode prevents switching,and no switching causes the image sticking. That is a problem.

[0020] To prevent the problem of image sticking due to movement of ionsin the liquid crystal, the positive and negative AC electric field isapplied usually. Though some charge transportable material such aspolyvinyl carbazole is served for bipolar transport, and such materialis less sensitive and is not used practically.

[0021] The conventional recording principle of such photo-addressabletype modulation element or photo-addressable type recording medium isdescribed in, for example, “O plus E, 1997, No. 206, pp. 115-119”, anddescribed herein under.

[0022] In detail, in a photo-addressable type modulation element ordisplay medium shown in FIG. 13A and FIG. 13B, a display element havinga type of threshold value and a light switching element are connected inseries and a voltage is applied on both ends. Because the respectivecapacity components of the display element 80 and the light switchingelement are approximately constant in respect to the light quantity, andthe impedance can be controlled by means of resistance component.

[0023] The display is controlled by controlling voltage division ratioof impedance of the display element 80 and light switching element 82.

[0024] Particularly, in the case that the impedance of the lightswitching element layer is lowered, namely in the case that lowresistance is used, “conductive state” electrical equivalent circuit isused as described in SID 96, APPLICATIONS DIGEST, pp. 59-60.

[0025] The term “conductive state” described herein means the state inwhich the resistance component of the light switching element layer isextremely reduced to a low impedance during irradiation with light, ormeans the state in which the resistance is reduced to an impedance solow as regarded as conductor as an electric equivalent circuit. In thenumerical expression, “conductive state” means the state that theresistance component of the light switching element layer is reduced toapproximately {fraction (1/100)} resistance component of the displayelement layer.

[0026] In this state, the effect of the capacitance component is verysmall and limited. Thereby, the division voltage becomes high, and asthe result the voltage exceeds the threshold voltage of the displayelement layer and the display is turned on. Because of such structure,it is required for the light switching element to have the resistancecomponent that is reduced to as small value as possible when irradiationis performed.

[0027] On the other hand, when the display is to be turned off, highimpedance is required, and a light switching element having theresistance component value that becomes low when irradiation with lightis performed and becomes high when irradiation with light is notperformed is necessary as described in Japanese Published UnexaminedPatent Application No. Hei 10-20328.

[0028] For example, a display medium in which a-Si:H is used for a lightswitching element and ferroelectric liquid crystal is used for a displayelement has been known as described in APPLIED OPTICS pp. 6859-6868.

[0029] The resistivity of the resistance component of a-Si:H falls from1.0×10¹¹ Ωcm to 1.0×10⁸ Ωcm with light radiation of 1 mW/cm². On theother hand, because the resistivity of the display element layer is>1.0×10¹⁰ Ωcm, the impedance of the light switching element layerbecomes conductive by irradiation with light.

[0030] In other words, because the light switching element becomesconductive when irradiation with light is performed, the voltage appliedto the display element layer becomes high, and as the result the displayis turned on. On the other hand, the impedance of the light switchbecomes high during non-irradiation with light, and the voltage appliedto the display element becomes low to an amplitude lower than thethreshold value of the display element, and as the result the display isturned off.

[0031] Therefore, a display medium is designed so that the lightswitching element becomes conductive and a voltage higher than thethreshold value is applied to the display element during irradiationwith light and the impedance of the light switching element layerbecomes high and a voltage lower than the threshold value is applied tothe display element during non-irradiation with light. Thereby, ON/OFFswitching of the display unit is controlled. The display unit isswitched between ON and OFF by operating the irradiation between ON andOFF selectively.

[0032] A photo-addressable type recording display medium in whichcholesteric liquid crystal is used for the display element and a-Si:H isused for the light switching element is proposed as a detachablerecording display medium provided with a display element formed of theabove-mentioned memory display material in, for example, SID 96,APPLICATIONS DIGEST pp. 59-62.

[0033]FIG. 14 shows the reflectance characteristic of thephoto-addressable type recording display medium to the externallyapplied voltage. In the case of this photo-addressable type recordingdisplay medium, the light switching element layer becomes conductive andthe division voltage becomes small, and the threshold value duringapplication of voltage becomes low (namely low threshold value Va) byirradiation with light. On the other hand, the resistance becomes highand the impedance becomes high, and the threshold value becomes high(namely high threshold value Vb) during non-irradiation with light.

[0034] Therefore, as shown in FIG. 14, the applied voltage is set to bein the relation Va<Vc<Vb, and the irradiation with light is selectivelyperformed for image recording. The division voltage due to fluctuationof the impedance is designed so as to be equal to or higher than thethreshold value when the display is ON, on the other hand so as to belower than the threshold value when the display is OFF.

[0035] However, in the case of such recording, because it takes a somelong time for the division voltage to approach the voltage divisionratio corresponding to the impedance, it is required that the recordingpulse is continuously applied until the division voltage approaches thevoltage division ratio corresponding to the impedance.

[0036] Furthermore, the much quantity of light is needed to render theimpedance of the light switching element layer low for light writing,and this is also a problem.

[0037] Heretofore, the irradiation with light is performed as much aspossible as long as the condition is allowable when the irradiationrenders the resistance component low. Particularly, in the case thatBi₁₂SiO₂₀ element or organic photosensitive element is used for thelight switching element, the resistance component during non-irradiationwith light is very large, and much light quantity is inevitably requiredto render the resistance of the light switching element layerconductive. For example, the resistance components of organicphotosensitive material is equal to or larger than 100 MΩ/cm² usually,or equal to or larger than 1 GΩ/cm² in some cases. The irradiation withlight of 1 mW/cm² or more is needed to render the resistance of thelight switching element layer conductive 1 GΩ/cm² or less.

[0038] Furthermore, the recording display medium of this type isinvolved in another problem that the pulse application time is long. Indetail, because the time constant of the light switching element ordisplay element layer during non-irradiation with light is long, it isrequired that a voltage should be applied continuously until the appliedvoltage is stabilized.

[0039] For example, in the case of a photo-addressable type modulationelement provided with the above-mentioned cholesteric liquid displayelement and a-Si:H light switching element that are combined together,because the resistance is approximately 10 MΩ/cm² and the capacitance isapproximately 4 nF/cm², the time constant is approximately 40 msresultantly, and approximately 160 ms is required to reach theresistance component ratio of the impedance.

[0040] On the other hand, in the case that organic photosensitivematerial is used for the light switching element, the resistance isapproximately 1 GΩ/cm² and the capacitance is approximately 1 nF/cm²usually under dark resistance, namely during non-irradiation with light.In this case, the time constant is inevitably as long as 1 second. Inaddition to the above-mentioned problem, the recording display medium isinvolved in another problem in the case that liquid crystal material isused for the display element. In detail, ions in the liquid crystal areremoved sometimes to improve performance of the display, at that timethe resistance component becomes a value equal to or larger than severaltens MΩ/cm² or and the capacitance component becomes a value in a rangefrom 0.1 nF/cm² to several tens nF/cm² because of the structuredescribed hereinabove, and the time constant becomes resultantly as longas several hundreds m seconds to 1 second inevitably.

[0041] Furthermore, the conventional recording method is involved inanother problem that only a positive image is obtained for a writingimage. The positive recording means a recording method that the displayis turned on brightly during irradiation with light and the display isturned off darkly during non-irradiation with light, and on the otherhand the negative recording means a recording method that the display isturned off darkly during non-irradiation with light and the display isturned on brightly during non-irradiation with light. When the displayis turned on, the state is in high reflectance in the case of thereflection type and the state is in high light transmittance in the caseof the transmission type. When the display is turned off, the state isin low reflectance in the case of the reflection type and the state isin low transmittance in the case of the transmission type.

SUMMARY OF THE INVENTION

[0042] The present invention has been made in view of the abovecircumstances and provides a photo-addressable type recording displayapparatus that is capable of high sensitivity recording and displayingwith a short writing pulse application time. Furthermore, the presentinvention provides a photo-addressable type recording display apparatusthat is capable of switching between positive display and negativedisplay easily.

[0043] The photo-addressable type recording display apparatus accordingto the present invention includes: a photo-addressable type recordingdisplay medium provided with a memory display element layer having apredetermined impedance and a light switching element layer having animpedance that is variable depending on irradiation with light laminatedon the display element layer and electrically connected in series to thedisplay element layer; a pattern light irradiation source thatirradiates the photo-addressable type recording display medium with apattern light that has been converted corresponding to imageinformation; a pulse voltage application part that applies apredetermined pulse voltage to the photo-addressable type recordingdisplay medium; and a driving control part that controls the pulsevoltage applied by the pulse voltage application part in accordance witha result of comparison between the predetermined impedance of thedisplay element layer and the impedance of the light switching elementlayer varied depending on the quantity of light from the pattern lightirradiation source for controlling a pulse waveform and a voltageamplitude of the voltage applied to the display element layer, therebycontrolling the display state of the photo-addressable type recordingdisplay medium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Preferred embodiments of the present invention will be describedin detail based on the followings, wherein:

[0045]FIG. 1A to FIG. 1E are graphs illustrating waveforms fordescribing the waveform change of the voltage waveform applied to thedisplay element layer due to impedance mismatching between the displayelement layer and the organic photoconductive switching element layer,

[0046]FIG. 2A to FIG. 2T are explanatory diagrams for describing thevoltage waveform applied to the display element layer and the thresholdvoltage,

[0047]FIG. 3 is a table for showing during irradiation with light/duringnon-irradiation with light, the comparative magnitude relation betweenthe time constant D of the display element layer and the time constant Sof the organic photoconductive switching element layer, the state of thedisplay element layer, and the display pattern corresponding to thevoltage waveform shown in FIG. 2A to FIG. 2T,

[0048]FIG. 4 is an explanatory diagram illustrating the schematicstructure of a photo-addressable type recording display apparatus inaccordance with an embodiment of the present invention,

[0049]FIG. 5 is a partial cross sectional view illustrating theschematic structure of the organic photoconductive switching elementlayer shown in FIG. 4,

[0050]FIG. 6 is a explanatory diagram illustrating the schematicstructure of the observation example 1 to the observation example 3,

[0051]FIG. 7 is a graph showing the relation between the reflectancechange and the applied voltage for the liquid crystal display elementcell of the observation example 1 during non-irradiation with light andduring irradiation with light,

[0052]FIG. 8 is an explanatory diagram illustrating the schematicstructure of the example 1 to the example 3,

[0053]FIG. 9 is a graph showing the relation between the reflectancechange and the applied voltage for the liquid crystal display elementcell of the comparative example 1 during non-irradiation with light andduring irradiation with light,

[0054]FIG. 10 is a graph showing the relation between the reflectancechange and the applied voltage for the liquid crystal display elementcell of the observation example 2 during non-irradiation with light andduring irradiation with light,

[0055]FIG. 11 is a graph showing the relation between the reflectancechange and the applied voltage for the liquid crystal display elementcell of the observation example 3 during non-irradiation with light andduring irradiation with light,

[0056]FIG. 12 is an explanatory diagram illustrating the generalschematic structure of a photo-addressable type recording display mediumprovided with a conventional display element and light switchingelement,

[0057]FIG. 13A and FIG. 13B are circuits that electrically representphoto-addressable type recording display medium provided with a displayelement and light switching element, and

[0058]FIG. 14 is a graph showing the relation between the appliedvoltage and the reflectance change for a conventional photo-addressabletype recording display medium during non-irradiation with light andduring irradiation with light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] In the present invention, a driving control unit controls thepulse waveform and the voltage amplitude of a voltage applied to thedisplay element layer depending on the comparative relation between theimpedance of the display element layer and the impedance of the lightswitching element layer that changes depending on the light quantity forirradiation incident from the light irradiation unit to thereby controlthe display state (namely ON/OFF of the display) of thephoto-addressable type recording display medium.

[0060] As the method for controlling the pulse waveform of the voltageapplied to the display element layer, for example, a pulse waveformforming method in which the arbitrary waveform is formed electricallyfor controlling or a method in which the impedance of the displayelement layer is matched with the impedance of the light switchingelement layer (impedance matching is performed) may be applied.Preferably, the method in which the impedance matching is performed maybe used.

[0061] Furthermore, at least one of the time constant of the displayelement layer and the time constant of the light switching element layeris controlled to thereby change the comparative magnitude relationbetween the impedance of the display element layer and the impedance ofthe light switching element layer for performing impedance matching. Thetime constant can be controlled by changing the resistance component orchanging the capacitance component.

[0062] For example, a laser light is incident on and absorbed in a lightswitching element to thereby cause phase change of the light switchingelement, the phase change causes the temperature rising, and thetemperature rising causes the resistance component change of the lightswitching element layer or causes the capacitance component change. Asthe result, the time constant can be controlled depending on theirradiation quantity and time of the laser light.

[0063] In another way, the light switching element layer formed ofphotoconductive material is used, the driving control unit controls thequantity of light for irradiation incident from the light irradiationunit, the charge quantity generated in the light switching element layercorrespondingly to the quantity of light is controlled to thereby changethe resistance component of the switching element layer, and as theresult the time constant can be controlled.

[0064] The structure in which the light switching element layer isformed of photoconductive material and the time constant is controlledis particularly preferable because the recording time and repeatabilityare reliable.

[0065] As described hereinabove, the display control is performed byimpedance matching in which mismatching between the impedance of thedisplay element layer and the impedance of the light switching elementlayer based on irradiation with light is adjusted so as to be matched.

[0066] Herein, the mismatching of impedance will be described.Generally, because the capacitance does not change regardless ofirradiation with light, the resistance component is changed for waveformcontrol by impedance matching.

[0067] In the case that a pulse is applied when the display elementlayer and the light switching element layer are connected each other inseries, the voltage waveform applied to the display element layer is notrectangular though a rectangular pulse is applied. The reason is thateach of the display element layer and the light switching layer can bealmost regarded as a circuit having the resistance component and thecapacitance component that are connected in parallel, and in the casethat such circuits are connected in series, the capacitance divisionthat is dependent of the capacitance component is predominant at first,but the resistance division that is dependent of the resistancecomponent becomes predominant with elapse of time.

[0068]FIG. 1A to FIG. 1E show the conceptual diagram of the voltageapplied to the display element layer corresponding to the voltageapplied to the light switching element layer in the case that thedisplay element layer and the light switching element layer areconnected each other in series. FIG. 1A to FIG. 1E show diagrams of thevoltage waveform that is applied to the display element layer obtainedwhen 5 rectangular pulses are applied, respectively. Examples in whichthe capacitance is almost equal are shown herein.

[0069] In the case that the impedance S of the light switching elementlayer is significantly larger than the impedance D of the displayelement layer (D<<S), the voltage waveform applied to the displayelement layer is similar to the differential waveform as shown in FIG.1A. The reason is usually that the light switching element layerfunctions as a capacitor because the resistance component becomes verylarge. An overshoot is seen after the final pulse.

[0070] In the case that the impedance D of the display element layer islarger than the impedance S of the light switching element layer (D<S),the voltage waveform is shown in FIG. 1B. At that time, usually theresistance component is several times to several tens times.

[0071] In the cast that the resistance component of the light switchingelement layer is lower than those in the above-mentioned cases and theimpedance D of the display element layer is equal to the impedance S ofthe light switching element layer (D=S), the voltage waveform is shownin FIG. IC in which the rectangular pulse is applied as it is. Ofcourse, even though the impedance of the light switching element layeris not exactly equal to the impedance of the display element layer, thatis, in the case that the resistance component is approximately ½ to 2times usually, the voltage waveform that is almost equal to the voltagewaveform that would be obtained when both impedances are equal can beobtained.

[0072] Furthermore, in the case that the resistance component of thelight switching element layer is lower and the impedance S of the lightswitching element layer is smaller than the impedance D of the displayelement layer (D>S), the voltage waveform is shown in FIG. 1D in whichthe voltage waveform is smoothed. Such voltage waveform is obtained whenthe resistance value is several tenth to several hundredth.

[0073] Furthermore, in the case that the resistance component of thelight switching element layer is further lower and the impedance S ofthe light switching element layer is significantly smaller than theimpedance D of the display element layer (D>>S), and the light switchingelement becomes equivalent to conductor. Therefore, the voltage waveformapplied to the display element layer becomes equal to the appliedvoltage pulse as shown in FIG. 1E. As a matter of course, in the casethat a functional film is provided, the voltage drops correspondingly,but the impedance of the functional film is smaller than those of thedisplay medium and the light switching element layer and the effect ofthe functional film is usually not so significant. Furthermore, eventhough the functional film is provided, the impedance changecorresponding to irradiation with light is not significant, and theeffect on the waveform applied to the display element is notsignificant.

[0074] Next, the recording display control of the photo-addressable typerecording display medium in which the voltage waveform as describedhereinabove is used will be described. FIG. 2A to FIG. 2T show schematicdiagrams of the voltage waveform applied to the display element layer ofthe photo-addressable type recording display medium for the case ofirradiation with light and for the case of non-irradiation with light.In this case, the applied voltage is actually AC voltage for driving,and the plural waveforms appear because positive/negative pulse isapplied. Herein, only the final waveform is shown for the purpose ofdescription.

[0075]FIG. 3 is a table listing irradiation with light/non-irradiationwith light, the comparative magnitude relation between the time constantD of the display element layer and the time constant S of the lightswitching element layer, ON/OFF state of the display element layer, andthe display pattern corresponding to the voltage waveform shown in FIG.2.

[0076] At first, the first case of the photo-addressable type recordingdisplay medium in which the time constant S of the light switchingelement layer is extremely larger than the time constant D of thedisplay element layer during non-irradiation with light (S>>D) and thetime constant S of the light switching element layer during irradiationwith light is approximately equal to the time constant of the displayelement layer (S≈D) or is smaller than the time constant D of thedisplay element layer (S<D) in the photo-addressable type recordingdisplay medium will be described. In this case, the driving control unitcontrols the voltage applied to the photo-addressable type recordingdisplay medium so that, during non-irradiation with light, the appliedvoltage equal to or higher than the threshold value is applied to thedisplay element layer continuously for a duration that is sufficientlyhigh to change the phase of the display element layer, and on the otherhand the driving control unit controls the voltage applied to thephoto-addressable type recording display medium so that, duringirradiation with light, the voltage having the voltage amplitude andvoltage application time that are not sufficient for the display elementlayer to reach the threshold value is applied to the display elementlayer. Otherwise, the driving control unit controls the voltage appliedto the photo-addressable type recording display medium so that thevoltage of the display element layer is substantially equal to or lowerthan the threshold voltage during irradiation with light due to waveformtransformation.

[0077] In other words, in the first case, the voltage waveform appliedto the display element layer during non-irradiation with light issimilar to the differential waveform as shown in FIG. 2A, the voltagewaveform applied to the display element layer during irradiation withlight is rectangular pulse waveform or rectangular pulse that isslightly deformed with rising to the right as shown in FIG. 2B.

[0078] Therefore, in the case of the first case, the driving controlunit applies the voltage so that the threshold value is equalized toV_(th) shown in FIG. 2A and FIG. 2B to thereby turn on the displayelement layer during non-irradiation with light and turns off thedisplay element layer during irradiation with light, and thus thenegative recording is performed. In other words, the applied voltage isset correspondingly to the waveform profile and threshold value as shownin FIG. 2A and FIG. 2B to thereby perform the negative recording. As theresult, by controlling as described hereinabove, the high sensitivityrecording apparatus having a wide margin can be obtained.

[0079] At that time, the driving control unit applies the pulse for aduration that is sufficiently long to change the phase of the displayelement layer. The duration that is sufficiently long to change thephase is, for example, approximately 1 ms to 10 ms in the case thatcholesteric liquid crystal is used for the display element layer, andequal to or shorter than 1 ms in the case that ferroelectric liquidcrystal is used.

[0080] Furthermore, in the case that the voltage profile during the timefrom dropping of the applied voltage to an amplitude equal to or lowerthan the threshold value to the turning-off of the display is selected,it is required to select the pulse application time so that the displayis not turned off. The time ranges usually from 1 ms to 100 ms.

[0081] The positive recording can be also realized. For performing thepositive recording, the driving control unit controls so that a voltagecorresponding to the threshold value V_(th) shown in FIG. 2B is appliedfor a duration of pulse application time that is sufficiently long toturn off the display in the voltage profile continuing from the timewhen the applied voltage drops to an amplitude equal to or lower thanthe threshold value to the time when the display is turned off.

[0082] In this case, if the time constant S of the light switchingelement layer is small, the voltage that is higher than the thresholdvalue may be applied for a duration that is sufficiently long to changethe phase. If the time constant D of the display element layer issmaller than the time constant S of the light switching element layer,because the waveform transformation occurs during display-off, theapplied voltage is controlled so that the effect on the display-on isreduced.

[0083] The effect of the waveform transformation is remarkable if theduration from the time when the voltage drops to an amplitude equal toor lower than the threshold value to the time when the voltage drops toan amplitude approximately equal to or lower than 4 V/μm is equal to orlonger than 10 ms, for example, the reflectance is reduced.

[0084] In this case, a positive image on which the background is brightand the image portion is dark can be displayed without forming areversed light pattern that is formed by reversing the image data.

[0085] Furthermore, in the case that the display is turned off bycontrolling so that the voltage of the display element layer is reducedto an amplitude equal to or lower than the threshold value due to thewaveform transformation to turn off the display, the applied voltage isset so that the threshold value is equalized to V_(th) shown in FIG. 2Aand FIG. 2B to thereby turn off the display during irradiation withlight, and thus the negative recording in which the display is OFFduring irradiation with light is possible.

[0086] Such situation can be realized by setting the duration, thatcontinues from the time when the voltage drops to an amplitude equal toor lower than the threshold value to the time when the voltage drops toan amplitude approximately equal to or lower than 4 V/μm, to a time of10 ms or longer in the case of cholesteric liquid crystal. This settingcan be achieved by setting the voltage to a desired value.

[0087] Next, the case of the photo-addressable type recording displaymedium in which the time constant S of the light switching element layeris larger than the time constant D of the display element layer (S>D)during non-irradiation with light, and the time constant S of the lightswitching element layer is almost equal to the time constant D of thedisplay element layer (S≈D) or is smaller than the time constant D ofthe display element layer (S<D) during irradiation with light in thephoto-addressable type recording display medium is described hereinunder. The driving control unit controls the voltage applied to thephoto-addressable type recording display medium so that a voltage thatis higher than the threshold voltage and has a magnitude sufficient tochange the phase is applied to the display element layer. Furthermore,the driving control unit controls the voltage applied to thephoto-addressable type recording display medium so that a voltage thatis equal to or higher than the threshold value is applied for a durationthat is sufficiently long to change the phase of the display elementlayer during irradiation with light, and controls the voltage applied tothe photo-addressable type recording display medium so that a voltage ofa magnitude that is sufficient to turn off the display element layer dueto the voltage drop that occurs in the duration from the time when thevoltage drops to an amplitude equal to or lower than the threshold valueto the time when the voltage is turned off for the voltage applicationtime during irradiation with light.

[0088] In the second case, the voltage waveform applied to the displayelement layer during non-irradiation with light is shown in FIG. 2C, inwhich the waveform shown in FIG. 2A is deformed. On the other hand, thevoltage waveform applied to the display element layer during irradiationwith light is shown in FIG. 2D, in which it is rectangular pulse orrectangular pulse that is deformed slightly upward to the right.

[0089] In the second case, for both cases of irradiation with light andnon-irradiation with light, the driving control unit applies a voltagethat is higher than the threshold voltage and is sufficient to changethe phase. However, during irradiation with light, the driving controlunit controls the voltage so that a voltage having an amplitude equal toor higher than the threshold value is applied for a duration that issufficiently long to change the phase, and, during non-irradiation withlight, controls the voltage to have an amplitude and duration ofapplication that is sufficient to turn off the display due to thevoltage drop from an amplitude equal to or lower than the thresholdvalue to the voltage being turned off. As the result, it is possible toperform the positive recording in which the display of the displayelement layer is turned on during irradiation with light and the displayof the display element layer is turned off during non-irradiation withlight.

[0090] In this case, cholesteric liquid crystal and capsulatedcholesteric liquid crystal, in which display is controllable due tosharpness that occurs when the voltage is turned off, are particularlypreferable as the display element layer. Organic photosensitive materialis used preferably for the light switching layer because the impedanceduring non-irradiation with light is high and effective.

[0091] Furthermore, the third case of the photo-addressable typerecording display medium in which the time constant S of the lightswitching element layer is approximately equal to the time constant ofthe display element layer (S≈D) during non-irradiation with light andthe time constant S of the light switching element layer is smaller thanthe time constant D of the display element layer (S<D) duringirradiation with light is described herein under. The driving controlunit controls the voltage applied to the photo-addressable typerecording display medium so that an applied voltage having an amplitudeequal to or higher than the threshold value is applied to the displayelement layer for a duration that is sufficiently long to change thephase of the display element layer during non-irradiation with light,and controls the voltage applied to the photo-addressable type recordingdisplay medium so that the voltage of the display element layer drops toan amplitude effectively equal to or lower than the threshold value dueto the waveform transformation during irradiation with light. The term“an amplitude effectively equal to or lower than the threshold value”means the state that the effect of high applied voltage equal to orhigher than the threshold value disappears because the voltage dropprofile is not sharp, and as the result the display performance becomespoor and the off state that is equivalent to the applied voltage equalto or lower than the threshold voltage results.

[0092] In the third case, the voltage waveform to be applied isrectangular pulse as shown in FIG. 2E during non-irradiation with light,and the voltage waveform is shown in FIG. 2F during irradiation withlight.

[0093] Therefore in the third case, the driving control unit applies avoltage equal to or higher than the threshold value for a duration thatis sufficiently long to change the phase during non-irradiation withlight to thereby turn on the display, and sets the threshold value sothat the display is turned off during irradiation with light due to thewaveform transformation. Thus, the negative recording is performed.

[0094] Furthermore, in the third case, the driving control meanscontrols the voltage applied to the photo-addressable type recordingdisplay medium so that a voltage equal to or higher than the thresholdvoltage is applied to the display element layer during non-irradiationwith light, and controls the voltage applied to the photo-addressabletype recording display medium so that an applied voltage equal to orhigher than the threshold value is applied to the display element layerfor a duration that is sufficiently long to change the phase of thedisplay element layer during irradiation with light. Thus, the positiverecording is also performed.

[0095] The fourth case of the photo-addressable type recording displaymedium in which the time constant D of the display element layer islarger than the time constant S of the light switching element layer(S>D) both during non-irradiation with light and during irradiation withlight is described herein under. The driving control unit controls thevoltage applied to the photo-addressable type recording medium so thatan applied voltage equal to or higher than the threshold value isapplied to the display element layer for a duration that is sufficientlylong to change the phase of the display element layer during irradiationwith light. Furthermore, the driving control unit controls the voltageapplied to the light writing time recording display medium so that avoltage is applied for a duration that is too short to change the phaseof the display element layer during non-irradiation with light.

[0096] In this case, the voltage waveform applied during non-irradiationwith light is shown in FIG. 2G, and the waveform applied duringirradiation with light is shown in FIG. 2H. As the result, the positiverecording is possible, in which a voltage equal to or higher than thethreshold value is applied for a duration that is sufficiently long tochange the phase during irradiation with light to thereby turn on thedisplay and the display is turned off during non-irradiation with lightdue to the waveform transformation.

[0097] Otherwise, in the fourth case, the driving control unit controlsthe voltage amplitude and application time of the voltage applied to thephoto-addressable type recording display medium so that the display ofthe display element layer is turned off due to the voltage drop thatoccurs from the time when the voltage applied to the display elementlayer drops to an amplitude equal to or lower than the threshold valueto the time when the voltage is turned off during non-irradiation withlight, and controls the voltage applied to the photo-addressable typerecording display medium so that a voltage equal to or higher than thethreshold value is applied to the display element layer for a durationthat is sufficiently long to change the phase of the display elementlayer during irradiation with light.

[0098] The fifth case of the photo-addressable type recording displaymedium in which the time constant S of the light switching element layeris smaller than the time constant D of the display element layer (S<D)both during irradiation with light and also during non-irradiation withlight is described herein under. The driving control unit controls thevoltage applied to the photo-addressable type recording display mediumso that application time is sufficiently shorter than the time that isrequired to change the phase of the display element layer or a voltagethat is not equal to or not higher than the threshold value that isrequired to change the phase of the display element layer is applied(that is, a voltage lower than the threshold value is applied) duringnon-irradiation with light, and controls the voltage applied to thephoto-addressable type recording display medium so that a voltage equalto or higher than the threshold voltage is applied to the displayelement layer during irradiation with light. In this case, the appliedvoltage is controlled so that the effect of the waveform transformationis reduced.

[0099] In this case, the voltage waveform applied during non-irradiationwith light is shown in FIG. 21, and the voltage waveform applied duringirradiation with light is shown in FIG. 2J. As the result, in the fifthcase, the positive recording is possible, in which the display is turnedoff during non-irradiation with light and the display is turned onduring irradiation with light by setting the applied voltage so that thethreshold value is V_(th) shown in FIG. 21 and FIG. 2J respectively.

[0100] Furthermore, in the fifth case, the driving control unit controlsthe voltage applied to the photo-addressable type recording displaymedium so that a voltage equal to or higher than the threshold value isapplied to the display element layer during irradiation with light andalso during non-irradiation with light, and controls the voltage so thatthe display element layer is maintained effectively equal to or lowerthan the threshold voltage due to the waveform transformation duringirradiation with light.

[0101] In this case, the voltage waveform applied during non-irradiationwith light is shown in FIG. 2K and the voltage waveform applied duringirradiation with light is shown in FIG. 2L. As the result, in the fifthcase, the negative recording is possible in which the display is turnedoff during irradiation with light and the display is turned on duringnon-irradiation with light by setting the applied voltage so that thethreshold value is V_(th) shown in FIG. 2K and FIG. 2L respectively.

[0102] Next, the sixth case of the photo-addressable type recordingdisplay medium in which the time constant S of the light switchingelement layer is larger than the time constant of the display elementlayer (S>D) during non-irradiation with light and the time constant S ofthe light switching element layer is smaller than the time constant D ofthe display element layer (S<D) during irradiation with light will bedescribed herein under. The driving control unit controls the voltageapplied to the photo-addressable type recording display medium so that avoltage equal to or higher than the threshold value is applied for aduration that is sufficiently long to change the phase of the displayelement layer during non-irradiation with light and also duringirradiation with light, and controls the voltage so that the displayelement layer is maintained effectively equal to or lower than thethreshold value due to the waveform transformation after the voltagedrops to an amplitude equal to or lower than the threshold value duringirradiation with light.

[0103] In this case, the voltage waveform applied during non-irradiationwith light is shown in FIG. 2M, and the voltage waveform applied duringirradiation with light is shown in FIG. 2N. As the result, the negativerecording is possible, in which the display is turned on duringnon-irradiation with light and the display is turned off duringirradiation with light by setting the applied voltage so that thethreshold value is V_(th) shown in FIG. 2M and FIG. 2N. At that time,because the display-on state is adversely affected if the duration whilethe voltage is being equal to or lower than the threshold value duringirradiation with light is too long, the duration while the voltage isbeing equal to or lower than the threshold value is set so that theadverse effect on the display-on state is reduced.

[0104] As the result, the driving control unit applies the voltage sothat the threshold value is V_(th) shown in FIG. 2M and FIG. 2N, and thenegative recording in which the display of the display element layer istuned on during non-irradiation with light and the display of thedisplay element layer is turned off due to the waveform transformationafter the voltage is turned off during irradiation with light isperformed.

[0105] In this case, the display element that is controllable of thereflectance based on the sharp characteristic that occurs when thevoltage is turned off, for example, cholesteric liquid crystal iseffective. It is preferable that the impedance matching is controlled sothat the duration from the time when the voltage drops to an amplitudeequal to or lower than the threshold value to the time when the voltageis turned off is approximately equal to or longer than, for example, 10ms.

[0106] Furthermore, in the sixth case, the driving control unit controlsthe voltage applied to the photo-addressable type recording displaymedium so that a voltage equal to or higher than the threshold voltageis applied for a duration shorter than the time that is required tochange the phase or a voltage lower than the threshold value is appliedduring non-irradiation with light, and controls the voltage applied tothe photo-addressable type recording display medium so that a voltageequal to or higher than the threshold value that is required to changethe phase of the display element layer is applied during irradiationwith light. Thereby, the positive recording is possible, in which thedisplay element layer is turned off during non-irradiation with lightand the display of the display element layer is turned on based on theapplied voltage equal to or higher than the threshold value duringirradiation with light.

[0107] In this case, the voltage waveform applied to the display elementlayer during non-irradiation with light is shown in FIG. 20, and thevoltage waveform applied to the display element layer during irradiationwith light is shown in FIG. 2P. Because the waveform transformationoccurs in off-characteristic during irradiation with light in the caseof this structure described hereinabove in which the threshold value isV_(th) shown in FIG. 20 and FIG. 2P, it is preferable that the appliedvoltage is set so that the adverse effect on the display-on is reduced.

[0108] The seventh case of the photo-addressable type recording displaymedium in which the time constant S of the light switching element layeris larger than the time constant D of the display element layer (S<D)during non-irradiation with light and the time constant of S of thelight switching element layer is smaller than the time constant of thedisplay element layer (S<D) during irradiation with light will bedescribed herein under. The driving control unit controls the voltageapplied to the photo-addressable type recording display medium so that avoltage equal to or higher than the threshold value is applied to thedisplay element layer for a duration that is sufficiently long to changethe phase due to overshooting that occurs when the voltage is turned offduring non-irradiation with light, and controls the voltage applied tothe photo-addressable type recording display medium so that the appliedvoltage of overshooting that occurs when the voltage is turned off islower than the voltage amplitude that is required to change the phase ofthe display element layer or so that the voltage is applied for aduration shorter than the time that is required to change the phase ofthe display element layer during irradiation with light.

[0109] In the seventh case, the voltage waveform applied to the displayelement layer during non-irradiation with light is shown in FIG. 2Q, andthe voltage waveform applied to the display element layer duringirradiation with light is shown in FIG. 2R.

[0110] As the result, in the seventh case, the driving control unitcontrols the applied voltage so that the threshold value is V_(th) shownin FIG. 2Q and FIG. R. Thereby, the negative recording can be performed,in which the display of the display element layer is turned on duringnon-irradiation with light and the display of the display element layeris turned off during irradiation with light because the voltage does notreach to the threshold value.

[0111] At that time, because the waveform transformation occurs duringirradiation with light, it is preferable to set the applied voltage sothat the adverse effect on the display-on is reduced. In the case thatcholesteric liquid crystal is used for the display element layer, theduration from the time when the voltage drops to an amplitude equal toor lower than the threshold value to the time when the voltage is turnedoff is set to an amplitude equal to or shorter than 10 ms to therebyreduce the adverse effect of the waveform transformation.

[0112] Furthermore, the eighth case of the photo-addressable typerecording display medium provided with a display element layer havingthe first threshold value V_(th-1) at which the display is turned offand the second threshold value V_(th-2) at which the display is turnedon in which the time constant S of the light switching element layer isapproximately equal to the time constant D of the display element layer(S≈D) or smaller than the time constant D of the display element layer(S<D) during irradiation with light will be described herein under. Thedriving control unit controls the voltage applied to thephoto-addressable type recording display medium so that an appliedvoltage having an amplitude equal to or higher than the first thresholdvalue V_(th-1) and equal to or lower than the second threshold valueV_(th-2) due to the overshooting that occurs when the display is turnedoff is applied to the display element layer during non-irradiation withlight, and controls the voltage applied to the photo-addressable typerecording display medium so that a voltage equal to or higher than thesecond threshold value V_(th-2) is applied to the display element layerduring irradiation with light. In this case, because the overshooting orwaveform transformation is not problematic as long as the overshootingor waveform transformation does not affect adversely on the displaycharacteristic, the time constant S of the light switching element layermay be slightly larger than the time constant D of the display elementlayer during irradiation with light.

[0113] In the eighth case, the voltage waveform applied to the displayelement layer during non-irradiation with light is shown in FIG. 2S, andthe voltage waveform applied to the display element layer duringirradiation with light is shown in FIG. 2T.

[0114] Therefore, in the eighth case, when the driving control unitapplies the voltage so that the threshold value is equalized to thesecond threshold value V_(th-2), the display of the display elementlayer is turned on during irradiation with light, and the display of thedisplay element layer is turned off during non-irradiation with lightbecause the overshooting is equal to or higher than the first thresholdvalue V_(th-1) and lower than the second threshold value V_(th-2).

[0115] Because the waveform transformation occurs during irradiationwith light while the display of the display element layer is beingturned on, the applied voltage is controlled so that the adverse effectof the waveform transformation on the display-on is reduced.Furthermore, the driving control unit controls the voltage to be appliedand the duration so that the overshooting does not exceed the firstthreshold value V_(th-1) and the display of the display element layer isnot turned off during irradiation with light while the display of thedisplay element layer is being turned on. For example, in the case thatcholesteric liquid crystal is used for the display element layer, thefirst threshold value V_(th-1) for display-off is approximately 4 V/μm,and the second threshold value V_(th-2) for display-on is approximately12 V/μm.

[0116] Though the case of one threshold voltage of the display elementlayer for reflectance or the case of two threshold values is describedhereinbefore in the description of the photo-addressable type recordingdisplay apparatus, the number of threshold value of the display elementlayer is by no means limited to one in the photo-addressable typerecording display apparatus described hereinabove having one thresholdvalue, but a display element layer having one or more threshold valuesmay be applied. Similarly, the number of threshold value is by no meanslimited to two in the photo-addressable type recording display apparatusdescribed hereinabove having two threshold values, but a display elementlayer having two or more threshold values may be applied.

[0117] The display element layer having one threshold voltage forreflectance means a display element layer containing a display mediumhaving only one threshold value Va in which the reflectance is differentdepending on the applied voltage between Va or lower and Va or higher.For example, smectic liquid crystal, ferroelectric liquid crystal,nematic liquid crystal, inorganic electrochromic element,electrophoretic element, electric field control type particle element,capsulated liquid crystals that are prepared by capsulating thesematerials, polymer network stabilized liquid crystal elements that areprepared by dispersing these materials in matrix polymer may be used asthe display medium.

[0118] For example, in the case of capsulated nematic liquid crystalelement, the reflectance is low under an applied voltage equal to orlower than the threshold voltage, and is high under an applied voltageequal to or higher than the threshold voltage.

[0119] The display element layer having two threshold voltages forreflection means a display element layer containing a display mediumhaving two threshold values V_(th-1) and V_(th-2) (V_(th-1)<V_(th-2)),in which the reflectance remains unchanged under the applied voltageequal to or lower than V_(th-1), the reflectance is low under theapplied voltage between V_(th-1) and V_(th-2), and the reflectance ishigh under the applied voltage equal to or higher than V_(th-2), or thereflectance is high under the applied voltage between V_(th-1) andV_(th-2), and the reflectance is low under the applied voltage equal toor higher than V_(th-2). In other words, as described herein, thedisplay element layer having two threshold voltages for reflection meansa display element layer containing a display medium in which thereflectance of the display medium changes differently at the twothreshold values V_(th-1) and V_(th-2).

[0120] The external voltage V that is equal to or higher than thethreshold value V_(th) is described herein under. It is assumed thatlayers other than the display element layer and the light switchingelement layer can be ignored electrically. At least the relationdescribed herein under holds for the case that the time constant S ofthe light switching layer is larger than the time constant D of thedisplay element layer (S>D).

(1/C _(D))(1/C _(D)+1/C _(S))>V _(th) /V

[0121] On the other hand, at least the relation described herein underholds for the case that the time constant S of the light switching layeris smaller than the time constant D of the display element layer (S<D).

R _(D)/(R _(D) +R _(S))>V _(th) /V

[0122] wherein C_(D) denotes the capacitance component of the displayelement layer, R_(D) denotes the resistance component of the displayelement layer, C_(S) denotes the capacitance component of the lightswitching element layer, and R_(S) denotes the resistance component ofthe light switching element layer.

[0123] The case that layers other than the display element layer and thelight switching element layer cannot be ignored electrically will bedescribed herein under. At least the relation described herein underholds for the case that the time constant S of the light switching layeris larger than the time constant of the display element layer (S>D).

(1/C _(D))(1/C _(D)+1/C _(S)+1/C _(ex))>V _(th) /V

[0124] At least the relation described herein under holds for the casethat the time constant S of the light switching layer is smaller thanthe time constant of the display element layer (S<D).

R _(D)/(R _(D) +R _(S) +R _(ex))>V _(th) /V

[0125] Wherein C_(ex) denotes the capacitance component of the layersother than the display element layer and the light switching elementlayer, and R_(ex) denotes the resistance component of the layers otherthan the display element layer and the light switching element layer.

[0126] As a matter of course, these relations are only for guide line,and may vary depending on the nonlinearity of the element, for example,the voltage dependency. Furthermore, it cannot be true for the case ofovershooting.

[0127] For example, the element such as cholesteric liquid crystal hasbeen known as such display medium. However, in the case of cholestericliquid crystal, it is required that the voltage is turned off sharplyafter voltage application to obtain high reflectance condition.

[0128] Furthermore, any of memory elements such as ferroelectriccapsulated liquid crystal element, cholesteric liquid crystal element,polymer network stabilized liquid crystal element that is formed ofcholesteric liquid crystal, polymer dispersion liquid crystal elementthat is formed of cholesteric liquid crystal, capsulated liquid crystalelement that is formed of cholesteric liquid crystal, electric fieldrotation element, electrophoretic element, electrophoretic typecapsulated element that is formed by capsulating electrophoreticelement, electric field moving type particle element, and polymernetwork stabilized element may be used preferably as the display medium.These materials are suitable for holding without power source, and themedium can be used in the state that the medium is detached from thewriting apparatus.

[0129] Among these materials, any one of polymer network stabilizedliquid crystal element, polymer dispersion liquid crystal element, andcapsulated liquid crystal element, that are formed of cholesteric liquidcrystal, is more preferably used.

[0130] A cholesteric liquid crystal element, polymer network stabilizedliquid crystal element, polymer dispersion liquid crystal element, andcapsulated liquid crystal element, that are formed of cholesteric liquidcrystal, are excellent in display controllability and effective becauseON/OFF of the display can be selected stably based on the sharpness thatoccurs when the voltage is turned off. The reason is that the profile ofvoltage drop that occurs when the display is turned off is controlledeasily by impedance matching control during irradiation with light.

[0131] Because the reflectance is controlled based on the sharpness ofthe voltage drop that occurs when the voltage is turned off in the caseof the cholesteric liquid crystal, the gradation is controllable.Furthermore, cholesteric liquid crystal can be used for a displayelement having the first threshold value V_(th-1) that is served forturning off the display and the second threshold value V_(th-2) that isserved for turning on the display when a voltage higher than it isapplied, and it is controllable based on the overshooting. As describedhereinabove, cholesteric liquid crystal element is the effectiveelement.

[0132] For fabrication of the light switching element, amorphous silicon(a-Si:H), CdS, or BSO may be used as inorganic photoconductive material,and diazo-base photosensitive material or phthalocyanine-base materialmay be used as organic photoconductive material. Among these materials,organic photoconductive material and BSO are preferably used because thevalue of the resistance component during non-irradiation with light islarge and the impedance is large.

[0133] Particularly, organic photoconductive material is preferably usedfor the light switching element layer because the impedance of organicphotoconductive material is high. Furthermore, ions are removedcompletely and the highly reliable liquid crystal has a large timeconstant. Another reason why organic photoconductive material is usedpreferably is that the photoconductive material having a large timeconstant is preferably used for impedance matching control. Thecontrollable range of the time constant based on irradiation with lightis wide, and the element can be designed easily. Furthermore, organicphotoconductive material is available at low cost, and is suitable formass-production.

[0134] The time constant is measured and determined by an impedancemeter, and in the measurement the display element and the lightswitching element are regarded as a parallel circuit having capacitancecomponent and resistance component respectively. The concept that theequivalent circuit of the respective elements is regarded as a parallelcircuit having the resistance component and the capacitance component isdescribed in, for example, “APPLIED OPTICS” 1992 Vol. 31, No. 32b,pp6859.

[0135] The present invention is easily applied in the case that afunctional layer, reflection layer, and light absorption layer arelaminated in addition to the display element layer and light switchingelement layer. As a matter of course, the present invention can beapplied to the case in which a color image is displayed by use of amultiple laminate.

[0136] A photo-addressable type recording display apparatus inaccordance with an embodiment of the present invention is roughlydivided into a recording unit 10 that displays an image, a light writingunit 12 that writes an image on the recording unit 20 with lightpattern, and a control unit 14 that controls the recording unit 10 andlight writing unit 12 as shown in FIG. 4. Herein, the light writing unit12 corresponds to the light irradiation unit of the present invention,and the control unit 14 corresponds to the driving control unit of thepresent invention.

[0137] The recording unit 10 is provided with a spatial light modulationelement 20 for constituting an image display surface and a driving unit22 for driving the spatial light modulation element 20. The spatiallight modulation element corresponds to the photo-addressable typerecording display medium of the present invention, and the driving unit22 corresponds to the application unit of the present invention.

[0138] The spatial light modulation element 20 has the structure inwhich a light incident side transparent substrate 30, a light incidentside transparent electrode layer 32, an organic photoconductiveswitching element layer 34, a liquid crystal display element layer 36,and a display side transparent electrode layer 38 are interposed in theorder of this arrangement between the light incident side transparentsubstrate 30 and a display side transparent substrate 31 that are facedeach other. Herein, the organic photoconductive switching element layer39 corresponds to the light switching element layer of the presentinvention, and the liquid display element layer 36 corresponds to thedisplay element layer of the present invention.

[0139] Known transparent substrate formed of a material such as glass orplastic may be used for the light incident side transparent substrate 30and the display side transparent substrate 31 properly, but flexiblesubstrate formed of a material such as polyester film, for example,polyethyleneterephthalate, or other films may be used. The transparentsubstrate having a thickness of approximately 100 μm to 500 μm is usedpreferably.

[0140] The light incident side transparent electrode layer 32 and thedisplay side transparent electrode layer 38 may be formed of electrodethat is light transmittable, and ITO electrode or the like is usedpreferably.

[0141] The liquid crystal display element layer 36 is a layer having amemory element that is selectively reflective or backward scatterable.The liquid crystal display element layer 36 has the structure in which aspacer is disposed between a pair of orientation films for orientingliquid crystal and liquid crystal material is filled in a spacepartitioned by the spacer. In the case that the liquid crystal displayelement layer 36 is rendered selectively reflective, cholesteric liquidcrystal is filled as the liquid crystal material, and otherwise in thecase that the liquid crystal display element layer 36 is renderedbackward scatterable, polymer dispersion liquid crystal that usesnematic liquid crystal as the liquid crystal material is filledpreferably. As a matter of course, cholesteric liquid crystal may bedispersed to form polymer dispersion liquid crystal, or cholestericliquid crystal may be capsulated preferably.

[0142] Because the light having the wavelength that is necessary fordisplaying is reflected and the light having the wavelength that isunnecessary for displaying is allowed to be transmitted in the case ofselective reflection and backward scattering, in the present embodiment,the organic photoconductive switching element layer 34 is provided onthe light incident side of the liquid crystal display element layer 36to thereby absorb the light that is transmitted through the liquidcrystal display element layer 36, and the absorbed light is used forlight switching.

[0143] The organic photoconductive switching element layer 34 of thepresent embodiment has a charge transport layer (CTL) 44 formed ofcharge transportive material, charge generation layers (CGL) 42 and 46provided on both upper side and under side of the charge transport layer(CTL) 44, a first electrode 40 provided on the under side of the underside charge generation layer (tail CGL) 42, and a second electrode 41provided on the upper side of the upper side charge generation layer(top CGL) 46 as shown in FIG. 5. Such dual CGL structure, in whichcharge generation layers are laminated on top and bottom of the chargetransport layer, allows AC voltage to be applied. Herein, the chargetransport layer 44 is formed of hole transportive material.

[0144] Such dual CGL structure allows the AC voltage to be applied. Indetail, when an organic photoconductive material having a dual CGLstructure is irradiated with light, hole h and free electron e aregenerated in the respective layers, namely the under side chargegeneration layer (CGL) 42 and the upper side charge generation layer(CGL) 46.

[0145] The hole h out of the hole h and free electron e generated in theupper side charge generation layer (CGL) 46 is transported to the chargetransport layer (CTL) 44, and combines with the free electron egenerated in the under side charge generation layer (CGL) 42. The freeelectron e generated in the upper side charge generation layer (CGL) 46impinges into the second electrode 41. Furthermore, the free electron eout of the hole h and free electron e generated in the under side chargegeneration layer (CGL) 42 combines with the hole h transported to thecharge transport layer (CTL) 44, and the hole h generated in the underside charge generation layer (CGL) 42 impinges into the first electrode40. Thereby, a current flows. Herein, in the case that the electricfield is inverted, a current flows in the inverted direction.

[0146] Organic material, that generates charges when irradiated withlight, such as perylene-base organic material, phthalocyanine-baseorganic material, bis-azo-base organic material, dithioketo pyrrole-baseorganic material, squarylium-base organic material, azulenium-baseorganic material, or thiapyrylium-polycarbonate-base organic materialmay be used as the charge generation layer material that forms the underside charge generation layer (CGL) 42 and the upper side chargegeneration layer (CGL) 46.

[0147] Dry film forming method such as vacuum evaporation method orspattering method or a method in which solvent or dispersion is usedsuch as spin coat method or dip method may be used as the method forfabricating the under side and upper side charge generation layers 42and 46 of the present embodiment. In any of these methods, substrateheating and severe process management are not necessary differently fromthe method for fabricating a-Si:H and photodiode.

[0148] The under side and upper side charge generation layers 42 and 46having a thickness of 10 nm to 1 μm, preferably 20 nm to 500 nm, arepreferably used. The film thickness thinner than 10 nm causesinsufficient photosensitivity and difficulty in manufacturing of evenproducts, and on the other hand the film thickness thicker than 1 μmcauses saturation of photosensitivity and easy separation of thelaminate due to in-film stress.

[0149] Furthermore, because it is required for the under side and upperside charge generation layers 42 and 46 to generate hole h and freeelectron e in the same quantity, it is required for both layers to havethe sensitivity to the wavelength, light quantity, and voltage in thesame level. Therefore, it is desirable that the under side and upperside charge generation layers 42 and 46 are formed of the same material.As a matter of course, different materials may be used as long as thesensitivity of these materials are in the same level.

[0150] Trinitrofluorene-base material, polyvinylcarbasole-base material,oxadiazole-base material, pylazoline-base, hydrazone-base material,stilbene-base material, triphenylamine-base material,triphenylmethane-base material, or diamine-base material may be used asthe charge transportive material of the charge transport layer (CGL) 44.The ion conductive material such as polyvinylalcohol orpolyethyleneoxide that contain added LiClO₄ may be used. Particularly,diamine-base material is preferably used because of its sensitivity andhole transportation capability.

[0151] Spin coat method or dip method in which solvent or dispersionmaterial is used may be employed as the method for fabricating thecharge transport layer in addition to the dry film forming method suchas vacuum evaporation method or spattering method. The film thickness ofthe charge transport layer ranges from 0.1 μm to 100 μm, preferably from1 μm to 10 μm. The film thickness thinner than 0.1 μm causes difficultyin impedance matching with the functional element and resultantly causesdifficulty in designing, and the above-mentioned range is preferablyused.

[0152] In addition to the above-mentioned structure, it is possible toadd the functional layer. For example, a functional layer for protectingimpingement of carrier disposed between an electrode and a chargegeneration layer is formed, a reflection layer or a shading layer isformed, DC component removing functional layer is formed, or afunctional layer that is served for these plural functions may beformed. These functional layers may be added as long as the functionallayer does not disturb the current flow.

[0153] Though the organic photoconductive switching element layer 34having the dual CGL structure is described in the present embodiment,not only the dual CGL structure but also organic photoconductive elementand amorphous silicon element having other structure may be used as longas the element layer having the structure is an optical functional layerthat is capable of light absorption and capable of photoelectrictransformation for converting the absorbed light to the charge inquantity equivalent to the absorbed light.

[0154] The driving unit 22 for driving the spatial light modulationelement 20 is provided with a connector 28 for connecting to theabove-mentioned light incident side transparent electrode layer 32 andthe display side transparent electrode layer 38 and a driving pulsegeneration unit 29. The driving pulse generation unit 29 detects atrigger signal for the driving waveform output supplied from a controlunit 14 that will be described hereinafter, generates a driving pulsebased on the detection of the trigger signal, and applies the drivingpulse on the light incident side transparent electrode layer 32 and thedisplay side transparent electrode layer 38 through the connector 28.Thereby, an electric filed is generated between the light incident sidetransparent electrode layer 32 and the display side transparentelectrode layer 38. Herein, the connector 28 is detachable.

[0155] The driving pulse generation unit 29 has, for example, a waveformmemory unit such as ROM and a DA conversion unit. The waveform memoryunit stores waveforms, for example, as shown in FIG. 2, and the DAconversion unit DA-converts the waveform read out from the ROM andgenerates a driving pulse. Any unit having different structure may beused as long as the unit can apply the driving pulse, for example, aunit having the structure that generates the pulse by use of an electriccircuit such as a pulse generation circuit may be used.

[0156] The light writing unit 12 is roughly divided into a patterngeneration unit 50 that generates a pattern correspondingly to an imagedata, and a light irradiation unit 52 that irradiates the light incidentside transparent substrate 30 of the spatial light modulation element 20with the pattern generated from the pattern generation unit 50 as thepattern of the light. The light writing unit 12 performs irradiationwith the pattern of the light formed correspondingly to the image datafrom the image display surface side of the spatial light modulationelement 20 based on the indication supplied from the control unit 14 forlight writing.

[0157] For example, a transmission type display such as TFT liquidcrystal display or simple matrix type liquid crystal display may be usedas the pattern generation unit 50. Any lighting unit may be used as thelight irradiation unit 52 as long as the lighting unit can be used toirradiate the spatial light modulation element 20 with a light such asfluorescent light, halogen lamp, or electroluminescence (EL) light.

[0158] Furthermore, the pattern generation unit 50 and the lightirradiation unit 52 may be formed separately as independent components,or may be formed combinedly as a unified component. In the case of theunified component, for example, an emission type display such as ELdisplay, CRT, or field emission display (FED) may be used. Other thanthese components, any illumination unit that is capable of controllingthe light quantity, wavelength, and irradiation pattern for irradiatingthe spatial light modulation element 20 may be used. As a matter ofcourse, the color of the light source is not limited to white, andchromatic light obtained by use of a filter may be used.

[0159] The control unit 14 is connected to external apparatuses such asa personal computer. The control unit 14 converts the image datasupplied from an external apparatus to the image data to be used fordisplaying and controls the light writing unit 12 and the driving unit22 synchronously. For example, when the image data is supplied from anexternal apparatus and a writing indication that indicates writing ofthe image data on the spatial light modulation element 20 is supplied tothe control unit 14, the control unit 14 supplies a trigger signalcorresponding to the comparative magnitude between the time constant Dof the liquid crystal display element layer 36 and the time constant Sof the organic photoconductive switching element layer 34 to the drivingunit 22, and supplies the image data to be used for displaying that hasbeen obtained by converting the input image data to the light writingunit 12.

[0160] Furthermore, the control unit 14 determines the magnitude andapplication time of the voltage that is to be applied on the spatiallight modulation element 20 by the driving unit 22 so that the thresholdvalue corresponds to the waveform determined correspondingly to thecomparative magnitude relation between the time constant D of the liquidcrystal display element layer 36 and the time constant S of the organicphotoconductive switching element layer 34 during irradiation with lightand during non-irradiation with light of the light writing unit 12, andsupplies the trigger signal for driving waveform output to the drivingunit 22.

[0161] The control unit 14 controls the driving of the light writingunit 12 and driving unit 22 so as to meet with the combination of theswitching between irradiation with light/non-irradiation with light thatis corresponding to the voltage waveform shown in FIG. 2, thecomparative magnitude relation between the time constant D of the liquidcrystal display element layer 36 and the time constant S of the organicphotoconductive switching element layer 34, and the ON/OFF switching ofthe liquid crystal display element layer 36.

[0162] For example, the cases that the D<<S during non-irradiation withlight and D>>S during irradiation with light in the comparativemagnitude relation between the time constant D of the liquid crystaldisplay element layer 36 and the time constant S of the organicphotoconductive switching element layer 34 will be described. Thecontrol unit 14 supplies the trigger signal to the driving unit 22 sothat an applied voltage equal to or higher than the threshold value Vafor a duration that is sufficiently long to change the phase is appliedon the liquid crystal display element layer 36 during non-irradiationwith light. On the other hand, during irradiation with light, thecontrol unit 14 controls the magnitude and the application time of thevoltage applied to the spatial light modulation element 20 so that avoltage lower than the threshold value Vb is applied for an applicationtime is applied on the liquid crystal display element layer 36.Otherwise, the control unit 14 controls so that the voltage equal to orlower than the threshold value b is applied on the liquid crystaldisplay element layer 36 due to the effect of the waveformtransformation.

[0163] Furthermore, the cases that the D<S during non-irradiation withlight and D≧S during irradiation with light in the comparative magnituderelation between the time constant D of the liquid crystal displayelement layer 36 and the time constant S of the organic photoconductiveswitching element layer 34 will be described. The control unit 14supplies the trigger signal to the driving unit 22 so that a voltagehigher than the threshold voltage Va having a magnitude that issufficiently high to change the phase is applied continuously on theliquid crystal display element layer 36. In this state, the control unit14 controls the voltage applied to the photo-addressable type recordingdisplay medium so that a voltage equal to or higher than the thresholdvalue is applied on the liquid crystal display element layer 36 for aduration that is sufficiently long to change the phase duringirradiation with light. The control unit 14 controls the voltage appliedto the photo-addressable type recording medium so that a voltage havinga voltage amplitude of the magnitude that turns off the display due tovoltage drop in the duration from the time when the voltage drops to anamplitude equal to or lower than the threshold value to the time whenthe voltage is turned off is applied for an application time on theliquid crystal display element layer 36.

[0164] Though two cases are described exemplarily herein, the controlunit 14 of the present embodiment controls the voltage applied to thephoto-addressable type recording display medium and also controls theirradiation with light by use of the light writing unit 12 not only inthe two cases described hereinabove but also in all the cases shown inFIG. 3.

[0165] Furthermore, the case in which the dual CGL organicphotoconductive structure is used as the organic photoconductiveswitching element layer 34 is described exemplarily in the presentembodiment, but as a matter of course the present invention is by nomeans limited to the dual CGL organic photoconductive structure, andorganic photoconductor having other structure or amorphous silicon maybe used as the organic photoconductive switching element layer 34.

EXAMPLE

[0166] At first, the observation experiment was carried out to determinethe condition of the application voltage and the application time beforethe example was fabricated. The observation experiment was carried outas described herein under to examine the effect of impedance matchingcontrol. A liquid crystal display element cell 37 having the samestructure as that of the liquid crystal display element layer 36 of thephoto-addressable type recording display medium, a functional layer, andan organic photoconductive switching element cell 35 having the samestructure as that of the organic photoconductive switching element layer34 were fabricated independently. The capacitance component and theresistance component of respective liquid crystal display element cell37 and organic photoconductive switching element cell 35 were measured.Then, the liquid crystal display cell 37 and the organic photoconductiveswitching element cell 35 were laminated so as to be connectedelectrically in series as shown in FIG. 6. The applied voltage appliedon the liquid crystal display element cell 37 and the reflectance changecorresponding to the applied voltage were measured by a reflectivitymeasuring device (X-Rite) during irradiation with light and duringnon-irradiation with light.

[0167] Glass substrates were formed for using as the light incident sidetransparent substrate 30 and the display side transparent substrate 31,and ITO films were formed for using as the light incident sidetransparent electrode layer 32 and the display side transparentelectrode layer 38. The ITO film was served also as the first electrode40 in the dual CGL structure.

[0168] The organic photoconductive switching element cell 35 had thedual CGL structure formed by successively laminating an under sidecharge generation layer 42, a charge transport layer 44, and an upperside charge generation layer 46, and in the observation experiment an Auelectrode 39 a was formed on the uppermost layer for connecting to theliquid crystal display element cell 37. The resistance was adjusted bycontrolling the film thickness of the charge generation layers 42 and 46and the charge transport layer 44, and the capacitance component wasadjusted by controlling the film thickness of the charge transport layer44.

[0169] The liquid crystal display element cell 37 had the structureformed by successively laminating a liquid crystal layer 47 that wasserved as the display element, a transparent electrode substrate 48, asubstrate 49, and a shading layer 39 b in the order from the displayside transparent electrode layer 38. The liquid crystal display elementcell 37 and the organic photoconductive switching element cell 35 weredisposed so that the shading layer 39 b of the liquid crystal displayelement cell 37 was faced to the Au electrode 39 a side of the organicphotoconductive switching element cell 35, and were disposed so that thereflectance could be measured from the display side transparentelectrode layer 38 side.

[0170] Cholesteric liquid crystal having a threshold value of fromapproximately 40 V/5 μm to 50 V/5 μm was used for the liquid crystallayer 47. A voltage of approximately 40 V/5 μm to 50 V/5 μm was appliedfor a duration of 5 ms or longer on the liquid crystal display elementcell 37, and then the voltage was dropped at a rate of approximately 50V/5 ms.

[0171] When the voltage was dropped to 10 V, the voltage became planarand the reflectance became as high as approximately 15% (display-on). Inthe case of the voltage drop rate equal to or slower than the valuedescribed hereinabove, the voltage became focal, and the reflectancebecame low at that time (display-off). The resistance component wasadjusted by changing the degree of purification.

[0172] The control unit 14 was structured so that a pulse generatorconnected to an amplifier applied the writing pulse. A halogen lightsource was used as the light writing unit 12.

[0173] An example was fabricated after the observation experiment, andsimilarly a comparative example was fabricated after the reflectancechange was measure by use of the reflectivity measuring device and thereflectance change was measure by use of the reflectivity measuringdevice. The observation example, the example, and the comparativeexample are described in this order herein under.

First Example

[0174] (1) Observation Example 1

[0175] At first, an ITO film that was served as the light incident sidetransparent electrode layer 32 was formed on a glass substrate that wasserved as the light incident side transparent substrate 30.Benzimidazole perylene (BZP) was vapor-deposited on the transparentsubstrate having the ITO film to form a BZP film having a film thicknessof approximately 0.08 μm and it was served as the under side chargegeneration layer 42.

[0176] A mixed solution containing 7.2% of biphenyldiamine-basematerial, 10.8% of polycarbonate bis-phenol-Z(poly(4,4′-cyclohexylidene-diphenylene-carbonate)), and 82% ofmonochlorobenzene was diluted doubly with monochlorobenzene to prepare adilute solution, and the dilute solution was coated to form a filmhaving a film thickness of approximately 3 μm by spin coat method, andthe film was served as the charge transport layer 44.

[0177] Furthermore, a BZP film having a film thickness of approximately0.08 μm was formed on the upper layer of the charge transport layer 44in the same manner as used to form the under side charge generationlayer 42 described hereinabove, the BZP film was served as the upperlayer side charge generation layer 46, an Au electrode was formed on theupper layer of the upper layer side charge generation layer 46 byspattering, and an organic photoconductive switching element cell 35 wasobtained.

[0178] The impedance caused when a light of 30 μW/cm² was irradiatedonto the organic photoconductive switching element cell 35 (duringirradiation with light) had the capacitance component of 1 nF/cm² andthe resistance component of 2 MΩ/cm², and the time constant wastherefore 2 ms. Furthermore, the impedance caused when irradiation witha light of 1 μW/cm² or lower was performed had the capacitance componentof 1.2 nF/cm² and the resistance component of 80 MΩ/cm², and the timeconstant was therefore 96 ms.

[0179] Furthermore, an ITO film was formed as the display sidetransparent electrode 38 on a glass substrate that was served as thedisplay side transparent substrate 31. On the transparent substratehaving the ITO film, spherical HAYABEADS L-25 (brand name of HayakawaRubber Co., Ltd.) having a diameter of 5 μm with adhesive waswet-sprayed, and another glass substrate having an ITO film was placedon it closely so that the ITO film was in contact with the spacer toform a cell frame. After the above-mentioned process was carried on in aroom temperature, the cell frame was heated to 110° C. for 30 min, andthe spacer was bonded to films to obtain an OPC liquid crystal cellframe.

[0180] Cholesteric liquid crystal, that selectively reflects blue colorlight, was injected into the OPC liquid crystal cell frame to obtain aliquid crystal display element cell 37. The injected cholesteric liquidcrystal was a mixture of 64.9% by weight of nematic liquid crystal ZLI4398 (brand name of Merck Japan Ltd.) having the positive ferroelectricanisotropy, 17.5% by weight of dextro-rotatory chiral CB 15 (brand nameof Merck Japan Ltd.), and 17.5% by weight of dextro-rotatory chiral CE 2(brand name of Merck Japan Ltd.). The impedance of the obtained liquidcrystal display element cell 37 had the capacitance component of 1nF/cm² and the resistance component of 50 MΩ/cm², and the time constantwas therefore 50 ms.

[0181] Herein, FIG. 7 shows the relation between the reflectance changeand the applied voltage in the case of the liquid crystal displayelement cell 37 of the observation example 1. The time constant of theliquid crystal display element cell 37 was 50 ms, and the time constantof the light writing switching element was 96 ms during non-irradiationwith light and 2 ms during irradiation with light.

[0182] In FIG. 7, the black rhomboid curve shows the reflectance changecharacteristic during non-irradiation with light, and the white trianglecurve shows the reflectance change during irradiation with light.

[0183] It is obvious from FIG. 7 that the liquid crystal display elementcell 37 has a threshold value around 280 V during non-irradiation withlight, but does not have a clear threshold value during irradiation withlight. Therefore, the liquid crystal display element cell 37 is turnedon when a voltage approximately equal to or lower than 100 V or avoltage approximately equal to or higher than 280 V is applied duringnon-irradiation with light, or when a voltage approximately equal to orlower than 100 V is applied during irradiation with light because thereflectance is approximately equal to or higher than 23%. On the otherhand, the liquid crystal display element cell 37 is turned off when avoltage approximately equal to or higher than 100 V and equal to orlower than 280 V is applied during non-irradiation with light or when avoltage equal to or higher than 100 V is applied during irradiation withlight.

[0184] The reflectance characteristic was measured in the case that afunctional element having the capacitance component of 40 nF/cm² and theresistance component of 2 KΩ/cm² was connected equivalently to thefunctional layer of a recording display medium as a functional layer,and almost the same result as obtained in the case of no functionalelement was obtained.

[0185] (2) Example 1

[0186] In the present example 1, the switching element cell formed oforganic photoconductive material was prepared as a light switchingelement to evaluate the waveform observed when AC voltage was applied.Furthermore, the memory display element and the switching element formedof organic photoconductive material were combined as a unified element,and an apparatus that was used for confirming that it was suitable fordisplaying an image.

[0187] At first, an ITO film was formed as the light incident sidetransparent electrode layer 32 on a glass substrate that was served asthe light incident side transparent substrate 30. Benzimidazole perylene(BZP) was vapor-deposited to form a BZP film having a film thickness ofapproximately 0.08 μm on the transparent substrate having the ITO filmto form the under side charge generation layer 42.

[0188] On the upper layer of the under side charge generation layer 42,a mixed solution containing 7.2% by weight of biphenyldiamine-basecharge transport agent, 10.8% by weight of Polycarbonate bisphenol-Z(poly(4,4′-cyclohexylidene-diphenylne carbonate)), and 82% by weight ofmonochlorobenzene that was doubly diluted with monochlorobenzene wascoated to form a film having a film thickness of approximately 3 μm byspin coat method, and this film was served as the charge transport layer44.

[0189] Furthermore, on the upper layer of the charge transport layer 44,a BZP film having a film thickness of approximately 0.08 μm was formedin the same manner as used for preparation of the above-mentioned underside charge generation layer 42, and this BZP film was served as theupper side charge generation layer 46. As the result, the organicphotoconductive switching element layer 34 having the dual CGL structurewas formed.

[0190] Furthermore, on the upper layer of the upper side chargegeneration layer 46, a metal-oxide shading film containingpolyvinylalcohol binder having a film thickness of approximately 1 μmwas coated and dried by spin coat method to form the shading layer 39 c.

[0191] Furthermore, on the upper layer of the shading layer 39 c,spherical spacer HAYABEADS L-25 (brand name of Hayakawa Rubber Co.,Ltd.) having a diameter of 5 μm with adhesive was wet-sprayed, and aglass substrate having an ITO film was placed in contact with the spacerclosely to form a cell frame. The above-mentioned process was carriedout in a room temperature, and the cell frame was heated to 110° C. for30 min to obtain the OPC liquid crystal cell frame in which the spacerand films were in contact closely.

[0192] In the OPC liquid crystal cell frame, cholesteric liquid crystal,that selectively reflects blue color light, was injected to form theliquid crystal display element layer 36. The injected cholesteric liquidcrystal was a mixture of 64.9% by weight of nematic liquid crystal ZLI4389 having the positive ferroelectric anisotropy (brand name of MerckJapan Ltd.), 17.5% by weight of dextro-rotatory chiral CB 15 (brand nameof Merck Japan Ltd.), and 17.5% by weight of dextro-rotatory chiral CE 2(brand name of Mer ck Japan Ltd.) as in the case of the above-mentionedobservation example 1. Herein, this spatial light modulation element 20was structured so as to be easily detachable from the apparatus body byuse of the connector.

[0193] The spatial light modulation element 20 having the structure asdescribed hereinabove was connected to the connector 28 as shown in FIG.8, a monochromatic equivalent type TFT liquid crystal 24 was placed incontact closely in order to enter an image, and the spatial lightmodulation element 20 was irradiated with the pattern light from theimage of the TFT liquid crystal 24. Simultaneously, 4 rectangularwaveform pulses of 50 Hz and 300 V was applied by the driving pulsegeneration unit 29, and an image was formed on the spatial lightmodulation element 20. The intensity of the light from the halogen lightsource 26 was adjusted so that the irradiation area of the organicphotoconductive switching element layer 34 was irradiated with the lightquantity of 30 μW/cm² and the non-irradiation area was irradiated withthe light quantity of 1 μW/cm².

[0194] (3) Comparative Example 1

[0195] The same structure as used in the observation example 1 was used.The irradiation with light quantity of 10 mW/cm² was performed so thatthe resistance component value equal to or smaller than {fraction(1/100)} of the liquid crystal display element cell 37 of theobservation example 1 was obtained, and as the result the resistancecomponent of 200 KΩ/cm² and capacitance component of 1 nF/cm² wereobtained. The same method as used in the observation example 1 was usedduring non-irradiation with light. The relation between the reflectanceand the applied voltage was obtained by use of this. The obtained resultis shown in FIG. 9.

[0196] In FIG. 9, the black rhomboid curve shows the reflectance changecharacteristic during non-irradiation with light, and the whiterectangle curve shows the reflectance change characteristic duringirradiation with light.

[0197] (4) Evaluation 1

[0198] Though the recording was possible in the observation example 1and also in the comparative example 1, the light quantity of 30 μW/cm²was sufficient for recording in the case of the observation example 1,that is, the observation example 1 was highly sensitive, on the otherhand the light quantity of 10 mW/cm² was required for recording in thecase of the comparative example 1. From this result, it was found thatthe sensitivity was significantly improved.

[0199] Therefore, in the example 1 in which the liquid crystal displayelement cell 37 and the organic photoconductive switching element cell35 of the observation example 1 were combined to form a unifiedcomponent, the light quantity of 30 μW/cm² was sufficient to record adesired image as in the case of the observation example 1. The recordingdisplay did not exhibit deterioration even after 1000 cycle repetition.The recording voltage equal to or higher than 280 V was sufficient andthe margin equal to or higher than 100 V was confirmed.

Second Example

[0200] (1) Observation Example 2

[0201] At first, an ITO film was formed as the light incident sidetransparent electrode layer 32 on a glass substrate that was served asthe light incident side transparent substrate 30. TiO-phthalocyanine wasvapor-deposited on the transparent substrate having the ITO film to forma film having a film thickness of approximately 0.04 μm, and the filmwas used as the under side charge generation layer 42.

[0202] On the upper layer of the under side charge generation layer 42,a diluted solution prepared by doubly diluting with monochlorobenzene amixture of 7.2% by weight of biphenyl-diamine-base material, 10.8% byweight of Polycarbonate-bisphenol-Z(poly(4,4′-cyclohexylidene-diphenylene carbonate)), and 82% by weight ofmonochlorobenzene was coated by spin coat method to form a film having afilm thickness of approximately 3 μm, and this film was used as thecharge transport layer 44.

[0203] Furthermore, on the upper layer of the charge transport layer 44,a phthalocyanine film having a film thickness of approximately 0.04 μmwas formed in the same manner as used for forming the above-mentionedunder side charge generation layer 42, and this film was used as theupper side charge generation layer 46. An Au electrode was formed byspattering on the upper layer of the upper side charge generation layer46 to obtain the organic photoconductive switching element cell 35.

[0204] The impedance of the organic photoconductive switching elementcell 35 under irradiation with light of 30 μW/cm² (during irradiationwith light) had the capacitance component of 0.6 nF/cm² and theresistance component of 64 MΩ/cm². Therefore, the time constant was 36ms. The impedance during irradiation with light equal to or lower than 1μW/cm² had the capacitance component of 0.6 nF/cm² and the resistancecomponent of 100 MΩ/cm². Therefore, the time constant was 60 ms.

[0205] Furthermore, an OPC liquid crystal cell frame was obtained in thesame manner as used in the above, cholesteric liquid crystal, thatselectively reflects blue color light, having the same composition asused in the above-mentioned observation example 1 was injected in theOPC liquid crystal cell frame to obtain the liquid crystal displayelement cell 37. The impedance of the obtained liquid crystal displayelement cell 37 had the capacitance component of 1 nF/cm² and theresistance component of 50 MΩ/cm².

[0206] Next, a functional element cell having the capacitance componentof 40 nF/cm² and the resistance component of 2 KΩ/cm² was connected. Thefunctional element cell was connected as the functional layer of theequivalently unified recording display medium, the capacitance andresistance did not affect adversely the liquid crystal display elementcell 37 and the organic photoconductive switching element cell 35.

[0207]FIG. 10 shows the relation between the applied voltage and thereflectance change of the liquid crystal display element cell 37 of theobservation example 2. The time constant of the liquid crystal displayelement cell 37 was 10 ms, the time constant of the light switchingelement was 60 ms during non-irradiation with light and 36 ms duringirradiation with light.

[0208] In FIG. 10, the black rhomboid curve shows the reflectance changecharacteristic during non-irradiation with light and the white squarecurve shows the reflectance change characteristic during irradiationwith light.

[0209] As obvious from FIG. 10, the liquid crystal display element cell37 has a threshold value around 290 V during non-irradiation with light,and has a threshold value around 250 V during irradiation with light.Therefore, the reflectance is equal to or higher than approximately 20%during irradiation with light in the range from 250 V to 290 V and thedisplay is turned on, and on the other hand the reflectance is equal toor lower than approximately 3% during non-irradiation with light and thedisplay is turned off.

[0210] (2) Example 2

[0211] In the example 2, a light switching element formed of organicphotoconductive material and a memory display element were preparedcombinedly, and an apparatus was fabricated to confirm that it wassuitably used as an image display apparatus.

[0212] At first, TiO-phthalocyanine was vapor-deposited on a transparentsubstrate having an ITO film to form a film having a film thickness ofapproximately 0.04 μm, and this film was used as the under side chargegeneration layer 42.

[0213] On the under side charge generation layer 42, a diluted solutionprepared by doubly diluting with monochlorobenzene a mixture of 7.2% byweight of biphenyl-diamine-base material, 10.8% by weight ofpolycarbonate-bisphenol-Z (poly(4,4′-cyclohexylidene-diphenylenecarbonate)), and 82% by weight of monochlorobenzene was coated by spincoat method to form a film having a film thickness of approximately 3μm, and this film was used as the charge transport layer 44.

[0214] Furthermore, on the upper layer of the charge transport layer 44,a phthalocyanine film having a film thickness of approximately 0.04 μmwas formed in the same manner as used for forming the above-mentionedunder side charge generation layer 42, and this film was used as theupper side charge generation layer 46. Thereby, the organicphotoconductive switching element layer 34 having the dual CGL structurewas formed.

[0215] Furthermore, on the upper layer of the upper side chargegeneration layer 46, a metal-oxide shading film containingpolyvinylalcohol binder having a film thickness of approximately 1 μmwas coated and dried by spin coat method to form the shading layer 39 c.

[0216] Furthermore, on the upper layer of the shading layer 39 c, an OPCliquid crystal cell frame was formed in the same manner as used in theexample 1, cholesteric liquid crystal having the same composition asused in the above-mentioned observation example 1, that selectivelyreflects blue color light, was injected into the OPC liquid crystal cellframe to form the liquid crystal display element layer 36.

[0217] The spatial light modulation element 20 having the structure asdescribed hereinabove was connected to the connector 28 as shown in FIG.8, a monochromatic equivalent type TFT liquid crystal 24 was placed incontact closely in order to enter an image, and the spatial lightmodulation element 20 was irradiated with the pattern light from theimage of the TFT liquid crystal 24 onto. Simultaneously, 4 rectangularwaveform pulses of 50 Hz and 280 V was applied by the driving pulsegeneration unit 29, and an image was formed on the spatial lightmodulation element 20. The intensity of the light from the halogen lightsource 26 was adjusted so that the irradiation area of the organicphotoconductive switching element layer 34 was irradiated with the lightquantity of 100 μW/cm² and the non-irradiation area was irradiated withthe light quantity of 1 nW/cm².

[0218] (3) Comparative Example 1

[0219] The same structure as used in the observation example 1 was used.The irradiation with light quantity of 100 mW/cm² was performed so thatthe resistance component value equal to or smaller than {fraction(1/100)} of the liquid crystal display element cell 37 of theobservation example 1 was obtained, and as the result the resistancecomponent of 100 KΩ/cm² and capacitance component of 1 nF/cm² wereobtained. The same method as used in the observation example 2 was usedduring non-irradiation with light.

[0220] (4) Evaluation 2

[0221] Though the recording was possible in the observation 2 and alsoin the comparative example 2, the light quantity of 100 μW/cm² wassufficient for recording in the case of the observation example 2, thatis, the observation example 2 was highly sensitive, on the other handthe light quantity of 100 mW/cm was required for recording in the caseof the comparative example 2. From this result, it was found that thesensitivity was significantly improved.

[0222] Therefore, in the example 2 in which the liquid crystal displayelement cell 37 and the organic photoconductive switching element cell35 of the observation example 2 were combined to form a unifiedcomponent, the light quantity of 100 μW/cm was sufficient to record adesired image as in the case of the observation example 2. The recordingdisplay did not exhibit deterioration even after 1000 cycle repetition.

Third Example

[0223] (1) Observation Example 3

[0224] At first, an ITO film that was served as the light incident sidetransparent electrode layer 32 was formed on a glass substrate that wasserved as the light incident side transparent substrate 30.Benzimidazole perylene (BZP) was vapor-deposited on the transparentsubstrate having the ITO film to form a BZP film having a film thicknessof approximately 0.02 μm and it was served as the under side chargegeneration layer 42.

[0225] On the under side charge generation layer 42, a charge transportfilm having a film thickness of approximately 3 μm was formed in thesame manner as used in the observation example 1, and this film was usedas charge transport layer 44.

[0226] Furthermore, a BZP film having a film thickness of approximately0.02 μm was formed on the upper layer of the charge transport layer 44in the same manner as used to form the under side charge generationlayer 42 described hereinabove, the BZP film was served as the upperlayer side charge generation layer 46, an Au electrode was formed on theupper layer of the upper layer side charge generation layer 46 byspattering, and an organic photoconductive switching element cell 35 wasobtained.

[0227] The impedance caused when the organic photoconductive switchingelement cell 35 was irradiated with a light of 100 μW/cm² (duringirradiation with light) had the capacitance component of 0.6 nF/cm² andthe resistance component of 7 MΩ/cm², and the time constant wastherefore 4.2 ms. Furthermore, the impedance caused when irradiationwith a light of μW/cm2 or lower was performed had the capacitancecomponent of 0.6 nF/cm² and the resistance component of 42 MΩ/cm², andthe time constant was therefore 25.2 ms.

[0228] Furthermore, an OPC liquid crystal cell frame was obtained in thesame manner as used in the above, and cholesteric liquid crystal, thatselectively reflects blue color light, having the same composition asthat used in the above-mentioned observation example 1 was injected inthe OPC liquid crystal cell frame to obtain the liquid crystal displayelement cell 37. The impedance of the obtained liquid crystal displayelement cell 37 had the capacitance component of 1 nF/cm² and theresistance component of 40 MΩ/cm². Therefore, the time constant was 40ms.

[0229] Next, a functional element cell having the capacitance componentof 40 nF/cm² and the resistance component of 2 KΩ/cm² was connected. Thefunctional element cell was connected as the functional layer of theequivalently unified recording display medium, the capacitance andresistance did not affect adversely the liquid crystal display elementcell 37 and the organic photoconductive switching element cell 35.

[0230]FIG. 11 shows the relation between the applied voltage and thereflectance change of the liquid crystal display element cell 37 of theobservation example 3. The time constant of the liquid crystal displayelement cell 37 was 40 ms, the time constant of the light switchingelement was 25.2 ms during non-irradiation with light and 4.2 ms duringirradiation with light.

[0231] In FIG. 11, the white rhomboid curve shows the reflectance changecharacteristic during non-irradiation with light and the black squarecurve shows the reflectance change characteristic during irradiationwith light.

[0232] As obvious from FIG. 11, the liquid crystal display element cell37 has a threshold value around 390 V during non-irradiation with light,and has the first threshold value around 240 V and the second thresholdvalue around 280 V during irradiation with light. Therefore, thereflectance is equal to or higher than approximately 20% duringirradiation with light in the range from 240 V to 280 V and the displayis turned on, and on the other hand the reflectance is equal to or lowerthan approximately 3% during non-irradiation with light and the displayis turned off. The first threshold value and the second threshold valuedescribed hereinabove indicate the threshold value of the liquid crystaldisplay element cell 37 itself, the second threshold value of the liquidcrystal display element cell 37 is the threshold value that appearsbecause the liquid crystal display element cell 37 is connectedelectrically in series to the organic photoconductive switching elementcell 35, and this threshold value is the third threshold value of thephoto-addressable type recording display medium.

[0233] Furthermore, in the range from approximately 280 V to 390 V, thereflectance is equal to or lower than 3% both during non-irradiationwith light and during irradiation with light and the display is turnedoff, however, in the range higher approximately 390 V, the reflectanceis equal to or higher than 20% during non-irradiation with light and thedisplay is turned on, and the reflectance is approximately equal to orlower than 3% during irradiation with light and the display is turnedoff.

[0234] In other words, only by changing the magnitude of the appliedvoltage, the recording can be switched between negative recording andpositive recording.

[0235] (2) Example 3

[0236] In the present example 3, the switching element cell formed oforganic photoconductive material was prepared as a light switchingelement to evaluate the waveform observed when AC voltage was applied.Furthermore, the memory display element and the switching element formedof organic photoconductive material were combined as a unified element,and an apparatus that was to be used for confirming the capability ofimage displaying was fabricated.

[0237] Benzimidazole perylene (BZP) was vapor-deposited on a transparentsubstrate having an ITO film in the same manner as used in the example 1to form a film having a film thickness of approximately 0.02 μm as acharge generation layer, and this film was used as the under side chargegeneration layer 42. Next, a charge transport film having a filmthickness of approximately 3 μm was formed as a charge transfer layer inthe same manner as used in the example 1, and this film was used as thecharge transport layer 44.

[0238] Furthermore, on the upper layer of the charge transport layer 44,a BZP film having a film thickness of approximately 0.02 μm was formedin the same manner as used for preparation of the above-mentioned underside charge generation layer 42, and this BZP film was served as theupper side charge generation layer 46. As the result, the organicphotoconductive switching element layer 34 having the dual CGL structurewas formed.

[0239] Furthermore, on the upper layer of the upper side chargegeneration layer 46, a metal-oxide shading film containingpolyvinylalcohol binder having a film thickness of approximately 1 μmwas coated and dried by spin coat method to form the shading layer 39 c.

[0240] Furthermore, on the upper layer of the shading layer 39 c, an OPCliquid crystal cell frame was formed in the same manner as used in theexample 1, cholesteric liquid crystal, that selectively reflects bluecolor light, having the same composition as used in the above-mentionedobservation example 1 was injected in the OPC liquid crystal cell frameto form the liquid crystal display element layer 36.

[0241] The spatial light modulation element 20 having the structure asdescribed hereinabove was connected to the connector 28 as shown in FIG.8, a monochromatic equivalent type TFT liquid crystal 24 was placed incontact closely in order to enter an image, and the spatial lightmodulation element 20 was irradiated with the pattern light from theimage of the TFT liquid crystal 24. Simultaneously, 4 rectangularwaveform pulses of 50 Hz and 300 V was applied by the driving pulsegeneration unit 29, and an image was formed on the spatial lightmodulation element 20. The intensity of the light from the halogen lightsource 26 was adjusted so that the irradiation area of the organicphotoconductive switching element layer 34 was irradiated with the lightquantity of 100 μW/cm² and the non-irradiation area was irradiated withthe light quantity of 1 nW/cm².

[0242] (3) Comparative Example 3

[0243] The above-mentioned comparative example 1 was used as thecomparative example 3.

[0244] (4) Evaluation 3

[0245] Though the recording was possible in the observation example 3and also in the comparative example 3, the light quantity of 100 μW/cm²was sufficient for recording in the case of the observation example 3,that is, the observation example 3 was highly sensitive, on the otherhand the light quantity of 10 mW/cm² was required for recording in thecase of the comparative example 3. From this result, it was found thatthe sensitivity was significantly improved.

[0246] Therefore, in the example 3 in which the liquid crystal displayelement cell 37 and the organic photoconductive switching element cell35 of the observation example 3 were combined to form a unifiedcomponent, the light quantity of 100 μW/cm² was sufficient to record adesired image as in the case of the observation example 3. The recordingdisplay did not exhibit deterioration even after 1000 cycle repetition.

[0247] As described hereinabove, according to the present invention, theeffect that the high sensitivity recording display is realized and therecording display is realized with short writing pulse application timeis obtained.

[0248] Furthermore, the effect that the switching between the positivedisplay and the negative display is realized easily is obtained.

[0249] The entire disclosure of Japanese Patent Application No.2000-177295 filed on Jun. 13, 2000 including specification, claims,drawings and abstract is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A photo-addressable type recording displayapparatus comprising: a photo-addressable type recording display mediumprovided with a memory display element layer having a predeterminedimpedance and a light switching element layer having an impedance thatis variable depending on irradiation with light laminated on the displayelement layer and electrically connected in series to the displayelement layer; a pattern light irradiation source that irradiates thephoto-addressable type recording display medium with a pattern lightthat has been converted corresponding to image information; a pulsevoltage application part that applies a predetermined pulse voltage tothe photo-addressable type recording display medium; and a drivingcontrol part that controls the pulse voltage applied by the pulsevoltage application part in accordance with a result of comparisonbetween the predetermined impedance of the display element layer and theimpedance of the light switching element layer varied depending on thequantity of light from the pattern light irradiation source forcontrolling a pulse waveform and a voltage amplitude of the voltageapplied to the display element layer, thereby controlling the displaystate of the photo-addressable type recording display medium.
 2. Thephoto-addressable type recording display apparatus as claimed in claim1, wherein the result of comparison between the impedance of the displayelement layer and the impedance of the light switching element layer isvaried by controlling a time constant of at least one of the displayelement layer and the light switching element layer.
 3. Thephoto-addressable type recording display apparatus as claimed in claim2, wherein the light switching element layer is formed ofphotoconductive material, and the driving control part controls thequantity of light from the pattern light irradiation source and therebycontrols the quantity of charge generated in the light switching elementlayer corresponding to the light quantity to thereby change a resistancecomponent of the switching element layer, and resultantly controls thetime constant.
 4. The photo-addressable type recording display apparatusas claimed in claim 2, wherein the photo-addressable type recordingdisplay medium has a time constant of the light switching element layerthat is extremely larger than a time constant of the display elementlayer during non-irradiation with light, and a time constant of thelight switching element layer is approximately equal to or smaller thana time constant of the display element layer during irradiation withlight, and the driving control part controls the voltage applied to thephoto-addressable type recording display medium so that an appliedvoltage equal to or higher than a threshold value is applied to thedisplay element layer for a duration that is sufficiently long to changethe phase of the display element layer during non-irradiation withlight, and so that the voltage of the display element layer issuppressed to a value lower than the threshold value, or the voltage ofthe display element layer is suppressed to a value equal to or lowerthan the threshold voltage due to the waveform transformation duringirradiation with light.
 5. The photo-addressable type recording displayapparatus as claimed in claim 2, wherein the photo-addressable typerecording display medium has a time constant of the light switchingelement layer that is larger than a time constant of the display elementlayer during non-irradiation with light, and the time constant of thelight switching element layer is approximately equal to or smaller thanthe time constant of the display element layer during irradiation withlight, and the driving control part controls the voltage applied to thephoto-addressable type recording display medium so that a voltage higherthan a threshold voltage having an amplitude that is sufficiently longto change the phase is being always applied to the display elementlayer, and so that a voltage equal to or higher than the threshold valueis applied to the display element layer for a duration that issufficiently long to change the phase during irradiation with light anda voltage having a voltage amplitude and duration of application thatare necessary for the display element layer to be turned off by avoltage drop from an amplitude equal to or lower than the thresholdvalue to a voltage being turned off is applied during non-irradiationwith light.
 6. The photo-addressable type recording display apparatus asclaimed in claim 2, wherein the photo-addressable type recording displaymedium has a time constant of the light switching element layer that isapproximately equal to a time constant of the display element layerduring non-irradiation with light, and the time constant of the lightswitching element layer is smaller than the time constant of the displayelement layer during irradiation with light, and the driving controlpart controls the voltage applied to the photo-addressable typerecording display medium so that a voltage equal to or higher than athreshold value is applied to the display element layer for a durationthat is sufficiently long to change the phase during non-irradiationwith light, and so that a voltage having an amplitude effectively equalto or lower than the threshold voltage is applied to the display elementlayer due to the waveform transformation during irradiation with light.7. The photo-addressable type recording display apparatus as claimed inclaim 2, wherein the photo-addressable type recording display medium hasa time constant of the light switching element layer that isapproximately equal to a time constant of the display element layerduring non-irradiation with light, and the time constant of the lightswitching element layer is smaller than the time constant of the displayelement layer during irradiation with light, and the driving controlpart controls the voltage applied to the photo-addressable typerecording display medium so that a voltage equal to or lower than athreshold voltage is applied to the display element layer duringnon-irradiation with light, and so that a voltage equal to or higherthan the threshold value is applied to the display element layer for aduration that is sufficiently long to change the phase of the displayelement layer during irradiation with light.
 8. The photo-addressabletype recording display apparatus as claimed in claim 2, wherein thephoto-addressable type recording display medium has a time constant ofthe light switching element layer that is larger than a time constant ofthe display element layer both during non-irradiation with light andduring irradiation with light, and the driving control part controls thevoltage applied to the photo-addressable type recording display mediumso that a voltage is applied to the display element layer for a durationthat is shorter than a duration to change the phase of the displayelement layer or a voltage smaller than the threshold value is appliedto the display element layer during non-irradiation with light, andcontrols so that a voltage equal to or higher than the threshold valueis applied to the display element layer for a duration that issufficiently long to change the phase of the display element layerduring irradiation with light.
 9. The photo-addressable type recordingdisplay apparatus as claimed in claim 2, wherein the photo-addressabletype recording display medium has a time constant of the display elementlayer that is larger than a time constant of the light switching elementlayer during both non-irradiation with light and irradiation with light,and the driving control part controls an amplitude and applicationduration of the voltage applied to the photo-addressable type recordingdisplay medium so that the display of the display element layer isturned off by the voltage drop from an amplitude equal to or lower thana threshold value to a voltage being turned off during non-irradiationwith light, and so that a voltage equal to or higher than the thresholdvalue is applied to the display element layer for a duration that issufficiently long to change the phase of the display element layerduring irradiation with light.
 10. The photo-addressable type recordingdisplay apparatus as claimed in claim 2, wherein the photo-addressabletype recording display medium has a time constant of the light switchingelement layer that is smaller than the time constant of the displayelement layer during both non-irradiation with light and irradiationwith light, and the driving control part controls the voltage applied tothe photo-addressable type recording display medium so that a voltage isapplied to the display element layer for a duration that is shorter thana duration to change the phase of the display element layer or a voltagesmaller than a threshold value is applied to the display element layerduring non-irradiation with light, and so that a voltage equal to orhigher than the threshold value is applied to the display element layerduring irradiation with light.
 11. The photo-addressable type recordingdisplay apparatus as claimed in claim 2, wherein the photo-addressabletype recording display medium has a time constant of the display elementlayer that is smaller than a time constant of the light switchingelement layer during both non-irradiation with light and irradiationwith light, and the driving control part controls the voltage applied tothe photo-addressable type recording display medium so that a voltageequal to or higher than a threshold value that is sufficiently high tochange the phase of the display element layer is applied to the displayelement layer during non-irradiation with light, and so that a voltagehaving an amplitude equal to or lower than the threshold voltage isapplied to the display element layer due to the waveform transformationcaused after the voltage is turned off during irradiation with light.12. The photo-addressable type recording display apparatus as claimed inclaim 2, wherein the photo-addressable type recording display medium hasa time constant of the light switching element layer that is larger thana time constant of the display element layer during non-irradiation withlight, and the time constant of the light switching element layer issmaller than the time constant of the display element layer duringirradiation with light, and the driving control part controls thevoltage applied to the photo-addressable type recording display mediumso that a voltage equal to or higher than a threshold value is appliedto the display element layer for a duration that is sufficiently long tochange the phase of the display element layer during bothnon-irradiation with light and irradiation with light, and so that avoltage having an amplitude effectively equal to or lower than thethreshold voltage is applied to the display element layer due to thewaveform transformation caused after the voltage drops to an amplitudeequal to or lower than the threshold value during irradiation withlight.
 13. The photo-addressable type recording display apparatus asclaimed in claim 2, wherein the photo-addressable type recording displaymedium has a time constant of the light switching element layer that islarger than a time constant of the display element layer duringnon-irradiation with light, and the time constant of the light switchingelement layer is smaller than the time constant of the display elementlayer during irradiation with light, and the driving control partcontrols the voltage applied to the photo-addressable type recordingdisplay medium so that a voltage is applied to the display element layerfor a duration that is shorter than a duration to change the phase ofthe display element layer or a voltage smaller than a threshold value isapplied to the display element layer during non-irradiation with light,and so that a voltage equal to or higher than the threshold value isapplied to the display element layer during irradiation with light. 14.The photo-addressable type recording display apparatus as claimed inclaim 2, wherein the photo-addressable type recording display medium hasa time constant of the light switching element layer that is larger thana time constant of the display element layer during non-irradiation withlight, and the time constant of the light switching element layer issmaller than the time constant of the display element layer duringirradiation with light, and the driving control part controls thevoltage applied to the photo-addressable type recording display mediumso that a voltage equal to or higher than the threshold value is appliedto the display element layer for a duration that is sufficiently long tochange the phase of the display element layer by overshooting causedwhile the voltage is being turned off during non-irradiation with light,and so that a voltage arising from overshooting caused while the voltageis being turned off, the voltage being lower than the voltage necessaryto change the phase of the display element layer, or so that a voltageis applied to the display element layer for a duration that is shorterthan a duration to change the phase during irradiation with light. 15.The photo-addressable type recording display apparatus as claimed inclaim 2, wherein the photo-addressable type recording medium comprises adisplay element layer having a first threshold value at which thedisplay is turned off and a second threshold value at which the displayis turned on when a voltage equal to or higher than the first thresholdvalue is applied, and has a time constant of the light switching elementlayer that is larger than a time constant of the display element layerduring non-irradiation with light, and the time constant of the lightswitching element layer is smaller than the time constant of the displayelement layer during irradiation with light, and the driving controlpart controls the voltage applied to the photo-addressable typerecording display medium so that a voltage arising from overshootingcaused while the voltage is being turned off is applied to the displayelement layer during non-irradiation with light, the voltage being equalto or higher than the first threshold value and equal to or lower thanthe second threshold value, and so that a voltage equal to or higherthan the second threshold value is applied to the display element layerduring irradiation with light.
 16. The photo-addressable type recordingdisplay apparatus as claimed in claim 1, wherein the display elementlayer comprises any one of a polymer network stabilized liquid crystalelement, polymer dispersion liquid crystal element, and capsulatedliquid crystal element that are formed of cholesteric liquid crystal.17. The photo-addressable type recording display apparatus as claimed inclaim 1, wherein the switching element layer is formed of organicphotoconductive material.